ANSWER SCHEME OF PREBOARD 1 -SCIENCE

 ANSWER KEY 

MARKING SCHEME

1) Dioptre (1)

2) Chlorofluro carbons (1)

3) Alkaline potassium permanganate

And Acidified potassium dichromate (½ + ½ )

4) h=+2 cm, u=-30cm f=-15cm

U = -30 cm

Screen should be placed at 30 cm in front of the mirror to obtain sharp image

 (2)

5) (a) Ability of eye to adjust its focal length to see hereby and distant objects

clearly (b) Focal length of eye lens decreases (1)

6) Food Chain Food Web

1) Sequential process of one Network of food chains with intercrosses

organism consuming the and linkages

other

2) Each Organism at a tropic Each organism at a tropic level receives

level receives food from one food from more than one group

group of organisms of organisms.

 (1 + 1)

7) For irrigation and generating electricity (1)

(1) Social problems - displacement of people without

proper rehabilitation and compensation ( ½ )

Economic problem - huge input without much benefits ( ½)

8) Structural Formula,

 1 – butyne (1)

 2 – butyne (1)

yes, both are isomers (½ )

Reason ( ½ )

9) (a) ethene being an unsaturated hydrocarbon add bromine and change to

colourless 1,2 – dibromoethane, (1)

but ethane is saturated hydrocarbon and no addition reaction with bromine (1)

(b) Reaction (1)10) Transparent ---- Light can pass through easily

eg: air, water ( ½ + ½ )

Opaque ---- does not allow light to pass through

eg: wood, stone etc ( ½ + ½ )

Transluscent ----- light passes only partially

eg: cloud, waxpaper ( ½ + ½ )

11) Grafting – brief description (1)

Cutting - brief description (1)

Layering - brief description (1)

12) Diagram – with labeling ,

Stigma, style, ovary, anthev, filament, petal, sepal (1 ½ + 1½ )

13) (a) Electronic Configurations,

Oxygen – 2, 6

Magnesium – 2,8,2 ( ½ + ½ )

(b) O2- --- 2,8

Mg2+ -- 2,8

O2- larger in size (1)

Reason.... (1)

14) [1] To increase the magnification of image (1)

 [2] To increase the sharpness of image (1)

 [3] To erect the final image (1)

15) [1] Temperature changes and rainfall failures (1)

 [2] Loss of immunity in humans (1)

 [3] Destruction of aquatic life and vegetation (1)

( Any other points also)

16) Definition (1)

 ray diagram (1)

Reason – lights of different colours travel with different speed in glass(1)

17) Sun as the only source of energy which the plants use for photosynthesis and

thereby to store food (1)

Flow of energy from sun into the biosphere (1)

Release of energy in the form of heat (1)

18) Atomic Number Electronic Group Period Configuration

 A 5 2,3 13 2 (½ + ½ )

 B 7 2,5 15 2 ( ½ + ½)

 C 10 2,8 18 2 ( ½ + ½)

19) [1] Essential for ecological balance

 [2] Maintain biodiversity

 [3] Prevention of flood or any other points (1 + 1 + 1 )

20) Each ray diagram with nature of image ( 1 + 1 + 1 + 1 + 1 )

 OR

 Explanation (3) Diagram (2)

21) [a] HIV (1)

 [b] Sexual contact, blood transfusion (1 + 1)

 [c] destroys white blood cells, reduce the immunity ( ½ + ½ )

 [d] use of condom,

 Using sterilized syringes ( Any one) (1)

 Or

 Diagram (3) Label (2)

22) [a] CH3-COOH ( ethanoic acid) (1)

 Conc. H2SO4

[b] CH3-COOH + C2H5OH → CH3-COOC2H5 + H2O (1)

[c] Ethyl ethanoate (1)

[d] Esterification (1)

[e] Saponication (1)

OR

[a] (i) nCH2=CH2 → ( −CH2 −CH2 −) (1)

(ii) CH3-COOH + NaHCO3 → CH3-COONa +H2O + CO2 (1)

[b] Presence of Ca2+ ions and Mg 2+ ions (1)

Formation of insoluble calcium and magnesium salts with soap (1)

Soap get wasted simply as it do not lather with soap (1)23) a. 2 points of difference (1+1)

 b. F1 generation is the generation of hybrids derived from a cross

 between two genetically different homozygous individuals.

 F2 generation is the generation produced as a result of

 interbreeding between the individuals of F1 generation. (1 + 1)

 c. Variations are difference found in structure, function, behaviors

 and genetic make up of different individuals of same parentage, variety,

 race and species. (1)

 or

 a) When the pollen of a flower falls on the stigma of the same flower the process

Is called as self pollination. If the pollen falls on the stigma of a different flower

The process is called as cross pollination. (1+1)

b) The transfer of pollen from anther to stigma is called pollination.

 The fusion of male and female gamete is called fertilization. (1+1)

 Pappaya, cucumber, water melon. (1)

24) Correct reasons (1+1+1+1+1)

 OR

Myopia, Correction using spectacles with concave lens. 1+1

 Ray Diagrams (1 ½ +1 ½)

 SECTION B

25. (a)

26.( c)

27. (a)

28. (c)

29.( c)

30. (a)

31.( a)

32.( b)33.(d)

34. (d)

35.( a)