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CBSEClass10Science

SamplePaper03(2019-20)

MaximumMarks:80

TimeAllowed:3hours

GeneralInstructions:

i. Thequestionpapercomprisesthreesections–A,BandC.Attemptallthesections.

ii. Allquestionsarecompulsory.

iii. Internalchoiceisgivenineachsection.

iv. AllquestionsinSectionAareone-markquestionscomprisingMCQ,VSAtypeand

assertion-reasontypequestions.Theyaretobeansweredinonewordorinonesentence.

v. AllquestionsinSectionBarethree-mark,short-answertypequestions.Thesearetobe

answeredinabout50-60wordseach.

vi. AllquestionsinSectionCarefive-mark,long-answertypequestions.Thesearetobe

answeredinabout80–90wordseach.

vii. Thisquestionpaperconsistsofatotalof30questions.

SectionA

1. Statethelawofconservationofmass.

2. Accountforthefollowing:Elementsofgroup18arecalledzerovalent.

3. Answerthequestionsthatfollowsonthebasisofyourunderstandingofthe

followingparagraphandtherelatedstudiedconcepts:

Bio-gasisanexcellentfuelasitcontainsupto75%methane.Itburnswithoutsmoke,

leavesnoresiduelikeashinwood,charcoalandcoalburning.Itisheatingcapacityis

high.Bio-gasisalsousedforlighting.Theslurryleftbehindisremovedperiodically

andusedasexcellentmanure,richinnitrogenandphosphorous.Thelarge-scale

utilisationofbio-wasteandsewagematerialprovidesasafeandefficientmethodof

LAKSHYA STUDY POINT

http://mycbseguide.com/


waste-disposalbesidessupplyingenergyandmanure.

i. Whattypeofsourceofenergyismentionedintheabovepicture?

ii. Doesthissourceofenergycancausepollution?Justifyyouranswerwithabrief

explanation.

iii. Writethetwoadvantagesofbiogasasfuel.

iv. WritethedifferentcomponentsofBiogas?

4. Followingquestionsarebasedonthetwotablesgivenbelow.Studythesetables

relatedtobloodsugarlevelsandanswerthequestionsthatfollow.

TableA(Bloodglucosechart)

MeanBloodGlucoseLevel(mg/dL)

Doctor'sadviceneeded 380

350

315

280

250

215

Good 180

150

Excellent 115



80

50

TableB(BloodReportofPatientXandY)

Timeofcheck BloodGlucoseranges(mg/dL)

PatientX PatientY

Beforebreakfast(Fasting) <100 70-130

Beforelunch,supperandsnack <110 70-130

Twohoursaftermeals <140 <180

Bedtime <120 90-15

Answerthefollowingquestions:

a. RefertoTableBshowingthebloodreportofthelevelsofglucoseofpatientsXand

Y.Inferthediseasewhichcanbediagnosedfromthegivendata.

b. Identifythehormonewhoselevelinthebloodisresponsiblefortheabovedisease.

c. Whichoneofthefollowingdietswouldyourecommendtotheaffectedpatient?

i. Highsugarandalow-fatdiet.

ii. Lowsugarandhighproteindiet.

iii. HighFatandlowfibrediet.

iv. Lowsugarandhighfibrediet.

d. RefertoTableAandsuggestthevalueofthemeanbloodglucoselevelbeyond

whichdoctor’sadviceisnecessary:

i. 80mg/dL

ii. 115mg/dL

iii. 50mg/dL

iv. 80mg/dL

5. ThecauseofAstigmatismis

a. Varyingcurvatureinverticallines

b. Varyingcurvatureinhorizontallines



c. Varyingcurvatureinbothhorizontalandverticallines

d. Noneofthese

OR

StatementA:Thefocallengthoftheeyelensisfixed,StatementB:Thecorneaofthe

eyecanbecomparedwiththeshutterofthecamera

a. NeitherstatementAnorstatementBistrue

b. BoththeStatementAandBaretrue

c. StatementBistrue,Aisfalse

d. StatementAistrue,Bisfalse

6. HowmanyNationalParksarethereinGujarat?

a. 5

b. 30

c. 24

d. 4

7. Whichoffollowingstatementisnotcorrectaboutelectricfuse

A.Itisalwaysconnectedinlivewire

B.Itisalwaysconnectedintheendofthecircuit

C.Thinnerthefusewire,greaterisitscurrentcapacity

D.Itscurrentcapacitymustbelessthanthemaximumcurrent

a. BandC

b. AandB

c. AandC

d. A,B,CandD

8. Bleachingpowderisusedinthepaperindustryasa

a. dehydratingagent



b. bleachingagent

c. reducingagent

d. dryingagent

OR

Anacidcanreactwith

a. PbSO4

b. AgCl

c. Na2SO4

d. Na2CO3

9. Matchthefollowingwiththecorrectresponse:

(1)Saprotrophs (A)Organismsobtainingfoodfromgreenplants

(2)Parasites (B)Organismsobtainingfoodfromhost

(3)Autotrophs (C)Organismsobtainingfoodfromdeadplantsandanimals

(4)Herbivores (D)Organismswhichpreparetheirownfood

a. 1-B,2-D,3-A,4-C

b. 1-C,2-B,3-D,4-A

c. 1-D,2-A,3-C,4-B

d. 1-A,2-C,3-B,4-D

10. Innaturalecosystems,decomposersinclude:

a. Onlybacteriaandfungi

b. Herbivoresandcarnivores



c. Onlymicroscopicanimals

d. Both(b)and(c)

11. Electropositivecharacterofelementsinaperiod___________fromlefttoright.

a. Increases

b. firstincrease,thendecrease

c. remainsthesame

d. decreases

12. AqueoussolutionsofzincsulphateandironsulphateweretakenintesttubesIandII

byfourstudentsA,B,CandD.Metalpiecesofironandzincweredroppedinthetwo

solutionsandobservationsmadeafterseveralhourswererecordedintheformof

tableasgivenbelow:

Thecorrectreportinghasbeenmadeinobservations:

a. A

b. C

c. D

d. B

13. Assertion:Inesterification,carboxylicacidandalcoholreactinthepresenceofacid

togiveester.



Reason:Esterificationisthereverseofsaponification.

a. AssertionisCORRECTbut,reasonisINCORRECT.

b. AssertionisINCORRECTbut,reasonisCORRECT.

c. BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof

theassertion.

d. BothassertionandreasonareCORRECTbut,reasonisNOTTHECORRECT

explanationoftheassertion.

14. Assertion:Whenthelengthofawireisdoubled,thenitsresistancealsogetsdoubled.

Reason:Theresistanceofawireisdirectlyproportionaltoitslength.

a. AssertionisINCORRECTbut,reasonisCORRECT.

b. BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof

theassertion.

c. BothassertionandreasonareCORRECTbut,reasonisNOTTHECORRECT

explanationoftheassertion.

d. AssertionisCORRECTbut,reasonisINCORRECT.

SectionB

15. (a)AnaqueoussolutionhasaPHvalueof7.0.Isthissolutionacidic,basicorneutral?

(b)IfH+concentrationofasolutionis molL-1whatwillbeitsP4value?

(c)WhichhashigherPHvalue:1-MHClor1-MNaOH

16. Givethecharacteristictestsfor .

OR

Zincpieceswereplacedineachofthefourtesttubescontainingdifferentsalt

solutionsasshownbelow

:

Acolourchangewouldbeobservedinsolutions:

17. ThepositionofthreeelementsA,BandCinthePeriodicTableareshownbelow:



Group16 Group17

- -

- A

- -

B C

i. StatewhetherAisametalornon-metal.

ii. StatewhetherCismorereactivethanA

iii. WillCbelargerorsmallerinsizethanB?

iv. Whichtypeofion,cationoranion,willbeformedbyelementA?

18. Whatismeantbyclottingofblood?Writeaflowchartshowingmajoreventstaking

placeinclottingofblood?

OR

Whatistheadvantageofdigestivecavity?

19. Whydoesthesunappearreddishinthemorning(aswellasinevening)?

20. Whatarefossils?Whatdotheytellusabouttheprocessofevolution?

21. Listintabularformthreedistinguishingfeaturesbetweencerebrumandcerebellum.

22. i. Thediagramshowsabarmagnetsurroundedbyfourplottingcompasses.Copy

thediagramandmarkthedirectionofthecompassneedleforeachofthecasesB,

CandD.

ii. WhichistheNorthpole,XorY?

23. Supposeyourparentshaveconstructedatworoomhouseandyouwantthatinthe

livingroomthereshouldbeaprovisionofoneelectricbulb,oneelectricfan,a

refrigeratorandaplugpointforappliancesofpowerupto2kilowatts.Drawacircuit

diagramshowingelectricfuseandearthingassafetydevices.



24. Inthefiguregivenbelow,anarrowbeamofwhitelightisshowntopassthrougha

triangularglassprism.Afterpassingthroughtheprism,itproducesaspectrumXYon

thescreen.

i. Namethephenomenon.

ii. StatethecoloursseenatXandY.

iii. Whydodifferentcoloursofwhitelightbendatdifferentanglesthroughaprism?

OR

Sudhafindsoutthatthesharpimageofwindowpaneofhersciencelaboratoryis

formedatadistanceof15cmfromthelens.Shenowtriestofocusthebuildingvisible

ofheroutsidethewindowinsteadofthewindowpanewithoutdisturbingthelens.In

whichdirectionwillshemovethescreentoobtainasharpimageofthebuilding?

Whatistheapproximatefocallengthofthislens?

SectionC

25. Howwillyougetmetalfromconcentratedore?

26. a. Namethegasevolvedduringfermentationprocess.

b. Whatroleisplayedbyyeastintheconversionofcanesugar(C12H22O11)to

ethanol?

c. Howcanthefollowingbeobtainedfrompureethanol?Expresschemicalreactions

bythechemicalequations.

i. Sodiumethoxide

ii. Ethylethanoate

iii. Ethanal

27. Whatisthedifferencebetweenanintercellularandintracellulardigestion?



28. Whyarebudding,fragmentationandregenerationallconsideredasasexualtypesof

reproduction?WithneatdiagramsexplaintheprocessofregenerationinPlanaria.

OR

Givereasons:

i. Placentaisextremelyessentialforfoetaldevelopment.

ii. Blockingofvasdeferenspreventspregnancy.

iii. Windactsasapollinatingagent.

iv. Useofcondomspreventspregnancy.

v. BlockingofFallopiantubespreventspregnancy.

29. Whatistheneedofcombiningdifferentresistors?Whatistheresultantresistance

whenanumberofresistancesareconnectedinseries?

30. Anairbubbleinwaterisshowninthefigure.Threeraysoflightareincidentonthe

airbubble.

Theangleofincidenceofray1ontheairbubbleisgreaterthanthecriticalangle.The

angleofincidenceofray2ontheairbubbleislessthanthecriticalangle.Ray3is

perpendiculartothesurfaceofthebubble.

i. Infigureatthepointwhereray1meetstheairbubble,mark

a. thenormaltothesurface

b. theangleofincidence

ii. Completetheraydiagramtoshowhowallthreerayscontinueaftertheymeetthe

airbubble.

iii. Definerefractiveindexofwater.Ifthespeedoflightinairis3 108ms-1andthe

speedoflightinwateris2.2 108ms-1.Calculatetherefractiveindexofwater.

OR



Anairbubbleinwaterisshowninthefigure.Threeraysoflightareincidentonthe

airbubble.

Theangleofincidenceofray1ontheairbubbleisgreaterthanthecriticalangle.The

angleofincidenceofray2ontheairbubbleislessthanthecriticalangle.Ray3is

perpendiculartothesurfaceofthebubble.

i. Infigureatthepointwhereray1meetstheairbubble,mark

a. thenormaltothesurface

b. theangleofincidence

ii. Completetheraydiagramtoshowhowallthreerayscontinueaftertheymeetthe

airbubble.

iii. Definerefractiveindexofwater.Ifthespeedoflightinairis3 108ms-1andthe

speedoflightinwateris2.2 108ms-1.Calculatetherefractiveindexofwater.



CBSEClass10Science

SamplePaper03(2019-20)

Answer

SectionA

1. Massisneverlostorgainedinchemicalreactions.Wesaythatmassisalways

conserved.Inotherwords,thetotalmassofproductsattheendofthereactionis

equaltothetotalmassofthereactantsatthebeginning.

2. Elementsofgroup18havecompletelyfilledoutermostshellandhavenotendencyto

gainorloseelectrons.Thus,elementsofthisgrouphavezerovalencyandarealmost

unreactive.So,theyarecalledzerovalent.

3. i. Itisarenewablesourceofenergy.

ii. No,Biogasisarenewable,aswellasaclean,sourceofenergy.Thegasgenerated

throughbio-digestionisnon-polluting;itactuallyreducesgreenhouseemissions.

iii. Thetwoadvantageofbiogasasafuelare:

a. Itburnswithoutsmoke,leavesnoresiduelikeashinwood,charcoalandcoal

burning.

b. Eco-friendly,cheaper,easytouse.

iv. Biogasisamixtureofmethane,hydrogen,carbondioxide,andhydrogensulphide.

4. a. Diabetes

b. (b)Insulin

c. (iv)lowsugarhighfibrediet

d. (i)180mg/dL

5. (c)Varyingcurvatureinbothhorizontalandverticallines

Explanation:Thedefectbywhichthepersonisnotabletodifferentiatehorizontal

andverticalposition,iscalledastigmatism.Itiscausedbyanerrorintheshapeofthe

cornea.Itcanbecorrectedbyusingcylindricallenses.

OR

(a)NeitherstatementAnorstatementBistrue,Explanation:Theimageontheretina

isformedbytwolenses–thecornea,whichisaconverginglenswhosefocallengthis



fixed,andtheeye-lens,whichisaconvexlenswhosefocallengthisnotfixedandcan

bevariedbychangingitsshape.

Inoptics,anapertureisaholeoranopeningthroughwhichlighttravels.Thepupilof

theeyeisitsapertureinopticsnomenclature;theirisisthediaphragmthatservesasthe

aperturestop.

6. (d)4,Explanation:TheGujaratstateofwesternIndiahasfourNationalParksand

twenty-oneWildlifeSanctuarieswhicharemanagedbytheForestDepartmentofthe

GovernmentofGujarat.

S.No.Nameof

NationalPark

Yearof

NotificationTotalArea(km²)

1 VansdaNationalPark 1979 23.99

2 BlackbuckNationalParkVelavadar 1976 34.53

3 GirForestNationalPark 1975 258.71

4 MarineNationalPark,GulfofKutch 1982 162.89

7. (a)BandCExplanation:

A.Afusewireisasafetywireconnectedinserieswiththelivewire,incaseofany

largecurrentsupplyormalfunctioningintheelectricconnectionsitmeltsandbreaks

theelectriccircuit.

B.Afusewireisconnectedinseriessoastopassthecurrenttotallythroughthefuse.

Itisnotconnectedintheendofthecircuit.

C.Therelationbetweenthicknessofawireandit'scurrentcarryingcapabilityisthat,

morethethicknessmorethecurrentawirecancarry.Sofusewiresaremadeof

sufficientthickness.Meansthinnerthefusewire,lesserisitscurrentcapacity.

D.Thefuseneedstoberatedslightlyhigherthanthemaximumoperatingcurrentof

theprotecteddevice,sothatthefusewon'tblowwhentheequipmentisused.

StatementBandCarenotcorrectaboutelectricfuse.

8. (b)bleachingagent,Explanation:Bleachingpowderisusedtobleachcottonand

linenintextileindustryandwoodpulpinpaperindustry.

OR



(d)Na2CO3,Explanation:AcidsreactwithmetalcarbonatestoevolveCO2gas.

9. (b)1-C,2-B,3-D,4-A,Explanation:Organismscanbegroupedasproducers,

consumersanddecomposersaccordingtothemannerinwhichtheyobtaintheir

sustenancefromtheenvironment.Producersorautotrophspreparetheirown

food.Consumerscanbeclassedasherbivores,carnivores,omnivoresand

parasites.Herbivoresobtainfooddirectlyfromgreenplants.Parasitesobtainfood

fromahost.

(1)Saprotrophs (C)Organismsobtainingfoodfromdeadplantsandanimals

(2)Parasites (B)Organismsobtainingfoodfromhost

(3)Autotrophs (D)Organismswhichpreparetheirownfood

(4)Herbivores (A)Organismsobtainingfoodfromgreenplants

10. (a)Onlybacteriaandfungi,Explanation:Innaturalecosystems,decomposers

includemicroorganisms,comprisingbacteriaandfungi,whichbreakdownthedeadremains

andwasteproductsoforganisms.Thesedecomposersbreakdownthecomplexorganic

substancesintosimpleinorganicsubstances.

11. (d)decreases,Explanation:Aswemovefromlefttorightinaperiod,thepositive

chargeincreasesduetogradualincreaseinthenumberofprotons.So,thevalence

electronsarepulledinmorestronglybythenucleusanditbecomesmoreandmore

difficultfortheatomstoloseelectrons.Thus,onmovingfromlefttorightinaperiod,

thetendencyofatomstoloseelectronsdecreasesi.eelectropositivecharacterof

elementsdecreases.

12. (b)C,Explanation:Fe+ZnSO4→NoreactionItisbecauseironislessreactivethanZinc.

Zn+FeSO4→ZnSO4+Fe

Thesolutionbecomescolourlessandblackirongetsdeposited.

13. (a)AssertionisCORRECTbut,reasonisINCORRECT.Explanation:Assertionis

CORRECTbut,reasonisINCORRECT.

14. (b)BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof

theassertion.Explanation:BothassertionandreasonareCORRECTandreasonisthe

CORRECTexplanationoftheassertion.

SectionB



15. (a)Thesolutionisneutralisnature.

(b)[H+]=

=10-2M

PH=

=-log[H+]

=-log[10-2]

=-(-2)log10=2

(c)1MNaOHsolution(basic)higherPH.Value

1MHClsolution(acidic)lowerPH.Value

16. Carbondioxide( )gasturnslimewatermilkywhenpassedthroughitduetothe

formationofinsolublecalciumcarbonate.

OR

ThecolourchangewilltakeplaceinIIIandIVaszincismorereactivethanironas

wellascopper.

17. i. Aisanon-metal.

ii. CislessreactivethanA.

iii. CwillbesmallerthanB.

iv. Awillformanion.

18. Abloodclotisformedwhenbloodcellsandfibrinstrandsclumptogether.Aclotthatblocksbloodflowiscalledathrombus.



OR

Adigestivecavitynotonlyisaplacewheredigestionoflargeparticlescantakeplace,

butitcanalsobeusedtostorefood.



19. Earthissurroundedbyenvelopeofgasescalledatmosphere.Atthetimeofsunrise(or

atsunset),lighthastotravelgreaterthickness[ABatsun-riseandBCatsunset]than

whatitcoverswhensunisoverheadatnoon[ithastotravelonlyDB].The

wavelengthofbluecolourisabouthalfthatofred,bluelightisscatterednearly=16

timesred.Asaresult,thesunappearsredatsunriseoratsunsetduetonegligible

scatteringofredincomparisonwithblue.

20. Preservedtracesoflivingorganismsarecalledfossilsfoundclosertothesurfaceof

eartharemorerecentinoriginthanthefossilswefindindeeperlayers.

Fossilsalsohelpustofindevolutionaryrelationbetweenorganisms.

21.

Cerebrum Cerebellum

1.Itisapartoftheforebrain. 1.Itisapartofthehindbrain.

2.Itformabout83%partofthetotal

brainweight.

2.Itformabout11%partofthetotal

brainweight.

3.Itisthelargestpartofthebrain.3.Itisthesecond-largestpartofthe

brain.

22. i.

ii. TheNorthPoleisX.

23. Thecircuitdiagramshowingtheelectricfuseandearthingassafetydevicesisas



follows:

24. i. Thephenomenoniscalleddispersion.

ii. X—VioletY—Red

iii. Differentcoloursofwhitelightbendthroughdifferentangleswithrespecttothe

incidentbeamoflightduetodifferenceinspeedoflightofdifferentwavelengths.

OR

LetusassumethatthewindowpaneisbetweenF2andinfinityfromthislensandthis

isaconvexlens.WeknowthatwhentheobjectisbetweeninfinityandF2,itsinverted

andrealimagesisformedbetween2Fand2F2.

Now,thedistantbuildingisatinfinityfromthelens.Itsimagewouldbeformedat2F.

So,thescreenneedstobemovedtowardsthelensinordertogetasharpimage.Its

approximatefocallengthis10cm(lessthanimagedistanceinearliercase).

SectionC

25. Extractionofthemetalfromtheconcentratedore.Themetalisextractedfromthe

concentratedorebythefollowingsteps:

(i)Conversionoftheconcentratedoreintoitsoxide.Thisisusuallydoneby

calcinationandroastingprocess.Themethoddependsuponthenatureoftheore.A

carbonateoreisconvertedintooxidebycalcinationwhileasulphideoreisconverted

intooxidebyroasting.

(ii)Conversionofoxidetometalbyreductionprocess.

(i)Conversionoforeintometaloxide:Itcanbedonebytwomethods

(a)Calcination:Itistheprocessofheatingtheconcentratedoreintheabsenceofair.

Thecalcinationprocessisusedtoremovedvolatileimpurities,waterfromthe



hydratedoresandtoconvertcarbonateoresintometaloxide.

Forexample:

(i)Zincoccursaszinccarbonateincalamine(ZnCO3).Theoreiscalcinated(heated

strongly)intheabsenceofairtoconvertittozincoxide.Duringcalcination,carbon

dioxideisexpelled.

ZnCO3 ZnO + CO2

Zinccarbonate(Calamineore) (Zinc.Oxide)

(ii)AluminiumoccursasAl2O3.2H2Oinitsbauxiteore.Whenthebauxiteoreis

calcined,watervapoursareexpelledandanhydrousaluminiumoxideisobtained.

Al2O3.2H2O Al2O3 + 2H2O

BauxiteOre AluminiumOxide

b)Roasting:Itistheprocessofheatingtheconcentratedorestronglyinthepresence

ofexcessair.Thisprocessisusedforconvertingsulphideorestometaloxide.

Forexample,zincoccursassulphideinzincblende(ZnS).Itisstronglyheatedin

excessofairwhenitformszincoxideandsulphurdioxidegasisexpelled.

2ZnS+3O2 2ZnO + 2SO2

Zincsulphide(Zincblendeore) ZincOxide

ii)Conversionofmetaloxidetometal:Themetaloxideformedaftercalcinationor

roastingisconvertedintometalbyreduction.Someofthemethodscommonlyused

forthereductionofmetaloxidestometalsarediscussedbelow:

I)Reductionbyheatingintheair:Metalslowinthereactivityseriescanbe

obtainedfromtheiroxidesbyheatinginair.Forexample,mercuryisobtainedfrom

cinnabar(HgS)orebythismethod.Themethodinvolvesthefollowingsteps:

i)Theconcentratedmercuricsulphide(cinnabaror)isroastedinairwhenmercuric

oxideisformed.



2HgS + 3O2 2HgO + 2SO2

Mercuricsulphide(Cinnabarore) Mercuricoxide

2HgO → 2Hg + O2

Mercuricoxide Mercuricmetal

ii)Mercuricoxideisheatedtoabout300oCanditdecomposestogivemercurymetal.

II)Chemicalreduction:Themetaloxidesfromcalcinationorroastingprocessesare

reducedtofreemetalbyusingchemicalagentslikecarbon,aluminium,sodiumor

calcium.

(a)Reductionwithcarbon:Theoxidesofmoderatelyreactivemetalslikezinc,

copper,nickle,tin,leadetc.canbereducedbyusingcarbonasreducingagent.Inthis

process,themetaloxideismixedwithcokeandheatedinafurnace.Carbonreduces

themetaloxidetofreemetal.

Fore.g.whenzincoxideisheatedwithcarbon,zincmetalisproduced.

ZnO + C Zn + CO

Zincoxide Reducingagent Zincmetal Carbonmonoxide

Similarly,leadisobtainedfromleadoxidebyheatingwithcarbon.

PbO + C → Pb + CO

Leadoxide Leadmetall

Cokeisverycommonlyusedasareducingagentbecauseitischeap.

(b)Reductionwithcarbonmonoxide:Metalscanbeobtainedfromoxidesby

reductionwithcarbonmonoxideinthefurnace.Forexample,ironisobtainedfrom

ferricoxidebyheatingwithcarbonmonoxide.

Fe2O3(s)+3CO 2Fe+3CO2

c)Reductionwithaluminium:Certainmetaloxidesarereducedbyaluminiumto

metals.Themethodisknownasaluminothermyorthermiteprocess.Forexample,

chromium,manganese,titanium,vanadiummetalsareobtainedbythereductionof



theiroxideswithaluminiumpowder.

3MnO2 + 4Al 3Mn + 2Al2O3

Manganeseoxide Manganese

Cr2O3 + 2Al 2Cr + Al2O3

Chromiumoxide Chromium

Similarly,chromiumisobtainedbyheatingchromiumoxidewithaluminium

powder.

(d)Reductionbyelectrolysisorelectrolyticreduction:Theoxidesofactivemetals

arecommonlyextractedbytheelectrolysisoftheirfusedsaltsusingsuitable

electrodes.Thisisalsocalledelectrolyticreduction.Theprocessofextractionof

metalsbyelectrolysisprocessiscalledelectrometallurgy.

Fore.g.,aluminiumoxideisverystableandaluminiumcannotbepreparedby

reductionwithcarbon.Itispreparedbytheelectrolysisofmoltenalumina(Al2O3).In

thisprocess,purealuminaisdissolvedinmoltencryolite(Na3ALF6)inanirontank

linedwithcarbon.Duringelectrolysis,thealuminiumions,Al3+arereducedat

cathode(bytheelectrons)toformaluminium.

Al3+ + 3e- → Al

Aluminiumion(frommoltenalumina) Aluminium(Atcathode)

Duringelectrolyticreductionofmoltensalts,themetalsarealwaysproducedatthe

cathode(negativeelectrode).

26. a. Thegasthatisevolvedisevolvedduringthefermentationprocessiscarbon

dioxide(CO2).Itisaccompaniedbybriskeffervescence.

b. Yeastisthesourceofenzymes-invertaseandzymase.Theseenzymesareneeded

forfermentationofcanesugar(C12H22O11)toethanol.

Invertasehelpsinbreakingsucrose(anaturallyoccurringcarbohydratepresent

incanesugar)intoitscomponents-glucoseandfructose.



Zymaseconvertsglucoseintoalcoholandcarbondioxide.

c. Therequiredchemicalreactionsforpureethanolareasfollows:-

i. Sodiumethoxide( )canbeobtainedfrompureethanolwhenitis

madetoreactwithsodium.Sodiumdisplaceshydrogenfromethanol.

ii. Ethylethanoatecanbeobtainedfrompureethanolbywarmingethanolwith

ethanoicacidinthepresenceofconc.sulphuricacid.Thisisesterification

reaction.

C2H5OH+CH3COOH +H2O

iii. Ethanalcanbeobtainedbyperformingthepartialoxidationofpureethanolin

theabsenceofwater.Achromiumbasedreagentsuchaschromiumtrioxide

canbeused.

C2H5OH+ O2 CH3CHO+H2O

27.

Intracellulardigestion Extracellulardigestion

1)Thedigestionoffoodoccurswithinthe

cell.

1)Thedigestionoccursinthecavityof

alimentarycanal.

2)Digestiveenzymesaresecretedbythe

surroundingcytoplasmintothefood

vacuole.

2)Digestiveenzymesaresecretedby

specialcellsintothecavityofalimentary

canal.

3)Digestiveproductsarediffusedintothe

cytoplasm.

3)Digestiveproductsdiffuseacrossthe

intestinalwallintovariouspartsofthe

body.

4)Itisalessefficientmethod.4)Itisamoreefficientmethodof

digestion.

5)Itoccursinunicellularorganisms. 5)Itoccursinmulticellularorganisms.

28. Budding,fragmentationandregenerationareallexampleofasexualreproduction

becausealloftheminvolveonlyoneparent.Maleandfemalegametesarenot



involvedinthereproduction.Thusinallofthethreeprocessnovariationis

produced.

Planariacanbecutintoanynumberofpiecesandeachpiecegrowsintoacomplete

organism.Thisprocessisknownasregeneration(seefig.)Regenerationiscarriedout

byspecialisedcellsknownasneoblast(adultstemcells).

Thesecellsproliferateandproducelargenumbersofcells.Fromthismassofcells,

differentcellsundergochangestobecomevariouscelltypesandtissues,givingriseto

wholeneworganismwithsameDNAcontentasitsparent.Thesechangestakeplace

inanorganisedmannerreferredtoasdevelopment.

OR

i. Placentaisatemporaryorganwhichisextremelyessentialforfoetaldevelopment

becauseithelpsinnutrition,respiration,excretion,etc.,ofthefoetusthroughthe

maternalsupply.Babyconnectswithplacentaviaumblicalcord.

ii. Blockingofvasdeferensisknownasvasectomywhichpreventspassageof

sperms,hence,thereisnofertilisationthusitpreventspregnancy.

iii. Anemophilyorwindpollinationisaformofpollinationwhere,windactsasa

pollinatingagentbecauseithelpsintransferofpollengrainsfromantherto

stigmaofaflower.e.g.wheat,ricecorn.



iv. Condomsasphysicalbarrier,whichprevententryofspermsintovagina,hence

preventspregnancy.

v. IfFallopiantubeisblockedsurgically,whichisbetterknownbythename

tubectomy,spermandeggdonotmeetandfuseandfertilisationdoesnottake

place.

29. Combinationofresistors:Resistorsofallvaluesofresistancesarenotavailable.Hence

resistorsareconnectedinanumberofwaystoincreaseordecreasethecombined

resistance.Therearetwodistinctwaysinwhichresistorscanbeconnected.Theyare

resistorsinseriesandresistorsinparallel.

Resistorsconnectedinseries

Resistorsaresaidtobeinseriesiftheyarejoinedendtoendsothatthesamecurrent

flowsthrougheachoneoftheminsuccession.Sincethereisasinglepathforthe

movingcharge,thesamecurrentmustflowthrougheachresistor.Lettheconductor

AB,BCandCDhavingresistancesequaltoR1,R2andR3respectively,bejoinedin

seriesandletthecurrentpassingthroughthembeI.

LetV1,V2andV3bethepotentialdifferencebetweentheendsofthefirst,secondand

thirdconductorrespectively.

ByOhm'slaw,

V1=IR1;V2=IR2andV3=IR3

IfVisthetotalpotentialdifferencebetweentheendsAandDandRsistheeffective

resistanceofthecombinationofalltheresistors,then

V=IRsButV=V1+V2+V3

ORIRs=IR1+IR2+IR3

ORRs=R1+R2+R3

Theaboveresultholdsgoodforanynumberofresistorsjoinedinseries.



Thuswhensomeresistorsarejoinedinseries,thetotalresistanceisthesumof

individualresistances.

30. i. Diagramforfirstpartisshownas:

ii. Thethreerayscontinueaftertheymeettheairbubbleareshownas:

iii. Refractiveindexofwaterisdefinedastheratioofthespeedoflightinavacuum

tothespeedoflightinwater.

Speedoflightinair, ms-1

Speedoflightinwater, ms-1

Therefore,Refractiveindex,

=1.4

OR



i. Diagramforfirstpartisshownas:

ii. Thethreerayscontinueaftertheymeettheairbubbleareshownas:

iii. Refractiveindexofwaterisdefinedastheratioofthespeedoflightinavacuum

tothespeedoflightinwater.

Speedoflightinair, ms-1

Speedoflightinwater, ms-1

Therefore,Refractiveindex,

=1.4


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