Class 10 Science: CBSE (Official) Sample Question Paper Solutions (2019-20) - 11 | Science Class 10 PDF Download

 Page 1


1 
Central Board of Secondary Education 
 
CLASS X  
SCIENCE:  086 
 
Marking Scheme for Sample Question Paper 2019-20 
 
SECTION A 
1 The property of self-linking of atoms of an element through covalent bonds in order to form straight 
chain, branched chains or cyclic chains of different sizes is called catenation. 
1 mark 
2 The valency of an element first increases and then decreases across a period. 1 mark 
3(a) The principle behind electric generator is Electromagnetic Induction- the phenomenon of producing 
current in a coil by changing the magnetic field associated with it. 
1 mark 
3(b) The polarity of the output alternating current changes every 1/100 seconds. 
Alternately: 
In 1 second the output (AC) completes 50 cycles. 
1 mark 
3(c) 
The suitability of Muppandal as a site for wind farms stems from its geographical location as it has access 
to the seasonal monsoon winds.  
1 mark 
3(d) City A  
It is more suitable for a wind-farm as there is consistently high wind-speed in that city throughout the 
year.  
0.5 mark 
0.5 mark 
4(a) Diabetes 1 mark 
4(b) Insulin 1 mark 
4(c) iv) low sugar high fibre diet 1 mark 
4(d) i) 180mg/dL 1 mark 
5 ii) pupils take time to adjust 
OR 
ii) refraction 
1 mark 
6 ii) = 40  O. 
V=IR, V = 4V, I = 100 mA = 0.1 A 
Hence R = V/I = 4/0.1 O = 40  O.  
1 mark 
7 i) volt-ampere 
Power = Voltage x Current. 
1 mark 
8 iv) Human faecal matter 
OR 
iv) The Industralist 
1 mark 
9 iii) Carbon monoxide 1 mark 
10 iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. 1mark 
11 i) Na
2
CO
3
 1mark 
Page 2


1 
Central Board of Secondary Education 
 
CLASS X  
SCIENCE:  086 
 
Marking Scheme for Sample Question Paper 2019-20 
 
SECTION A 
1 The property of self-linking of atoms of an element through covalent bonds in order to form straight 
chain, branched chains or cyclic chains of different sizes is called catenation. 
1 mark 
2 The valency of an element first increases and then decreases across a period. 1 mark 
3(a) The principle behind electric generator is Electromagnetic Induction- the phenomenon of producing 
current in a coil by changing the magnetic field associated with it. 
1 mark 
3(b) The polarity of the output alternating current changes every 1/100 seconds. 
Alternately: 
In 1 second the output (AC) completes 50 cycles. 
1 mark 
3(c) 
The suitability of Muppandal as a site for wind farms stems from its geographical location as it has access 
to the seasonal monsoon winds.  
1 mark 
3(d) City A  
It is more suitable for a wind-farm as there is consistently high wind-speed in that city throughout the 
year.  
0.5 mark 
0.5 mark 
4(a) Diabetes 1 mark 
4(b) Insulin 1 mark 
4(c) iv) low sugar high fibre diet 1 mark 
4(d) i) 180mg/dL 1 mark 
5 ii) pupils take time to adjust 
OR 
ii) refraction 
1 mark 
6 ii) = 40  O. 
V=IR, V = 4V, I = 100 mA = 0.1 A 
Hence R = V/I = 4/0.1 O = 40  O.  
1 mark 
7 i) volt-ampere 
Power = Voltage x Current. 
1 mark 
8 iv) Human faecal matter 
OR 
iv) The Industralist 
1 mark 
9 iii) Carbon monoxide 1 mark 
10 iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. 1mark 
11 i) Na
2
CO
3
 1mark 
2 
Central Board of Secondary Education 
 
12 iii) C 
  OR 
iii) Q and R 
1mark 
13 i) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark 
14 iv) Assertion is false but reason is true. 1 mark 
 
SECTION B 
15 (i) It turns yellow due to formation of lead oxide and Reddish brown fumes evolve. 
(ii) Thermal decomposition reaction. 
                            heat 
(iii) 2Pb(NO
3
)
2    
                  2PbO  + 4NO
2  
+  O
2 
 
0.5 + 0.5 
mark 
 
  1 mark         
  1 mark 
16 (i) Sodium bicarbonate/Sodium hydrogencarbonate/ baking soda and its formula is NaHCO
3
 
                            heat 
(ii)  2NaHCO
3
                     Na
2
CO
3 
+ CO
2 
+ H
2
O 
(iii) It is used in fire extinguisher and for baking. (any one) 
OR  
(i) Add 10 mL of concentrated sulphuric acid slowly to 90 mL of water with constant stirring. 
Dilution of acid is a highly exothermic process. If water is added to concentrated sulphuric acid, heat 
generated causes the mixture to splash leading to burns and the glass container can break.  
(ii) Decreases per unit volume. 
0.5 + 0.5 
mark 
1 mark 
1 mark 
 
1 mark 
1 mark 
1 mark 
17 Electronic configuration of     X: 2,8,2,    Y: 2,8,6 
Both X and Y belong to 3rd period. 
Ionic bond will be formed. 
Reason: X will lose 2 electrons and Y will gain 2 electrons to complete their octet and become stable. 
Formula is XY    
0.5 + 0.5 
mark 
0.5 mark 
1 mark 
0.5 mark 
18 A food chain showing Ist tropic level (½ mark), II
nd
 tropic level (½ mark), III
rd
 tropic level 
 (½ mark) and IV
th
 tropic level (½ mark). 
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted 
According to the 10% law, the amount of energy available will not be sufficient for the survival of the 
organism in the 5th trophic level. 
                                                               OR 
• Large jar filled with water, oxygen, food and aquatic plants and animals. 
• Oxygen/oxygen pump. 
• Fish food. 
• Aquatic plants/Producers provide O
2
 during photosynthesis. 
• Aquatic animals/Consumers release CO
2
 for the process of photosynthesis. 
• Decomposers are also important for natural cleaning of the aquarium. 
(0.5 mark for each point) 
2 mark 
 
 
1 mark 
 
 
 
 
 
 
3 mark 
Page 3


1 
Central Board of Secondary Education 
 
CLASS X  
SCIENCE:  086 
 
Marking Scheme for Sample Question Paper 2019-20 
 
SECTION A 
1 The property of self-linking of atoms of an element through covalent bonds in order to form straight 
chain, branched chains or cyclic chains of different sizes is called catenation. 
1 mark 
2 The valency of an element first increases and then decreases across a period. 1 mark 
3(a) The principle behind electric generator is Electromagnetic Induction- the phenomenon of producing 
current in a coil by changing the magnetic field associated with it. 
1 mark 
3(b) The polarity of the output alternating current changes every 1/100 seconds. 
Alternately: 
In 1 second the output (AC) completes 50 cycles. 
1 mark 
3(c) 
The suitability of Muppandal as a site for wind farms stems from its geographical location as it has access 
to the seasonal monsoon winds.  
1 mark 
3(d) City A  
It is more suitable for a wind-farm as there is consistently high wind-speed in that city throughout the 
year.  
0.5 mark 
0.5 mark 
4(a) Diabetes 1 mark 
4(b) Insulin 1 mark 
4(c) iv) low sugar high fibre diet 1 mark 
4(d) i) 180mg/dL 1 mark 
5 ii) pupils take time to adjust 
OR 
ii) refraction 
1 mark 
6 ii) = 40  O. 
V=IR, V = 4V, I = 100 mA = 0.1 A 
Hence R = V/I = 4/0.1 O = 40  O.  
1 mark 
7 i) volt-ampere 
Power = Voltage x Current. 
1 mark 
8 iv) Human faecal matter 
OR 
iv) The Industralist 
1 mark 
9 iii) Carbon monoxide 1 mark 
10 iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. 1mark 
11 i) Na
2
CO
3
 1mark 
2 
Central Board of Secondary Education 
 
12 iii) C 
  OR 
iii) Q and R 
1mark 
13 i) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark 
14 iv) Assertion is false but reason is true. 1 mark 
 
SECTION B 
15 (i) It turns yellow due to formation of lead oxide and Reddish brown fumes evolve. 
(ii) Thermal decomposition reaction. 
                            heat 
(iii) 2Pb(NO
3
)
2    
                  2PbO  + 4NO
2  
+  O
2 
 
0.5 + 0.5 
mark 
 
  1 mark         
  1 mark 
16 (i) Sodium bicarbonate/Sodium hydrogencarbonate/ baking soda and its formula is NaHCO
3
 
                            heat 
(ii)  2NaHCO
3
                     Na
2
CO
3 
+ CO
2 
+ H
2
O 
(iii) It is used in fire extinguisher and for baking. (any one) 
OR  
(i) Add 10 mL of concentrated sulphuric acid slowly to 90 mL of water with constant stirring. 
Dilution of acid is a highly exothermic process. If water is added to concentrated sulphuric acid, heat 
generated causes the mixture to splash leading to burns and the glass container can break.  
(ii) Decreases per unit volume. 
0.5 + 0.5 
mark 
1 mark 
1 mark 
 
1 mark 
1 mark 
1 mark 
17 Electronic configuration of     X: 2,8,2,    Y: 2,8,6 
Both X and Y belong to 3rd period. 
Ionic bond will be formed. 
Reason: X will lose 2 electrons and Y will gain 2 electrons to complete their octet and become stable. 
Formula is XY    
0.5 + 0.5 
mark 
0.5 mark 
1 mark 
0.5 mark 
18 A food chain showing Ist tropic level (½ mark), II
nd
 tropic level (½ mark), III
rd
 tropic level 
 (½ mark) and IV
th
 tropic level (½ mark). 
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted 
According to the 10% law, the amount of energy available will not be sufficient for the survival of the 
organism in the 5th trophic level. 
                                                               OR 
• Large jar filled with water, oxygen, food and aquatic plants and animals. 
• Oxygen/oxygen pump. 
• Fish food. 
• Aquatic plants/Producers provide O
2
 during photosynthesis. 
• Aquatic animals/Consumers release CO
2
 for the process of photosynthesis. 
• Decomposers are also important for natural cleaning of the aquarium. 
(0.5 mark for each point) 
2 mark 
 
 
1 mark 
 
 
 
 
 
 
3 mark 
3 
Central Board of Secondary Education 
 
19 
  
  
1+1+1 
mark 
 
 
 
 
20 Let purple trait be represented by: PP           White trait be : pp 
          parental          PP  X  pp 
                                          ? 
           F
1 
                  Pp X Pp    (Selfing) 
           F
2
 
                                         ? 
Gametes P p 
P PP Pp 
p Pp pp 
 
Visible characters of F1 progeny all flowers are purple coloured and in F2 progenies 3 are purple 
coloured and 1 is white coloured flower              
 
 
0.5 + 1 + 
0.5 mark 
 
 
 
 
 
0.5 + 0.5 
mark 
21 When growing plant shoot tip detects light a hormone called auxin is synthesised in the shoot tip which 
is sensitive to light. 
Auxin diffuses towards the shady side of the stem. 
It stimulates the growth of cells on the shady side of the plant which causes bending of the plant to the 
other side.  
This gives the appearance that the stem of the plant bends in the direction of light.  
1 mark 
0.5mark   
1 mark  
 
0.5 mark   
22 (i) Range of distance should be 0 cm to < 12 cm. 
(ii) The image will larger than the object. 
 
 (0.5 mark to be deducted if no arrows marked or wrongly marked arrows) 
(iii) Image will be at 24cm in front of the mirror or the image is formed at C 
0.5 mark 
 
 
 
1.5 mark 
 
 
 
 
 
1 mark 
Page 4


1 
Central Board of Secondary Education 
 
CLASS X  
SCIENCE:  086 
 
Marking Scheme for Sample Question Paper 2019-20 
 
SECTION A 
1 The property of self-linking of atoms of an element through covalent bonds in order to form straight 
chain, branched chains or cyclic chains of different sizes is called catenation. 
1 mark 
2 The valency of an element first increases and then decreases across a period. 1 mark 
3(a) The principle behind electric generator is Electromagnetic Induction- the phenomenon of producing 
current in a coil by changing the magnetic field associated with it. 
1 mark 
3(b) The polarity of the output alternating current changes every 1/100 seconds. 
Alternately: 
In 1 second the output (AC) completes 50 cycles. 
1 mark 
3(c) 
The suitability of Muppandal as a site for wind farms stems from its geographical location as it has access 
to the seasonal monsoon winds.  
1 mark 
3(d) City A  
It is more suitable for a wind-farm as there is consistently high wind-speed in that city throughout the 
year.  
0.5 mark 
0.5 mark 
4(a) Diabetes 1 mark 
4(b) Insulin 1 mark 
4(c) iv) low sugar high fibre diet 1 mark 
4(d) i) 180mg/dL 1 mark 
5 ii) pupils take time to adjust 
OR 
ii) refraction 
1 mark 
6 ii) = 40  O. 
V=IR, V = 4V, I = 100 mA = 0.1 A 
Hence R = V/I = 4/0.1 O = 40  O.  
1 mark 
7 i) volt-ampere 
Power = Voltage x Current. 
1 mark 
8 iv) Human faecal matter 
OR 
iv) The Industralist 
1 mark 
9 iii) Carbon monoxide 1 mark 
10 iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. 1mark 
11 i) Na
2
CO
3
 1mark 
2 
Central Board of Secondary Education 
 
12 iii) C 
  OR 
iii) Q and R 
1mark 
13 i) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark 
14 iv) Assertion is false but reason is true. 1 mark 
 
SECTION B 
15 (i) It turns yellow due to formation of lead oxide and Reddish brown fumes evolve. 
(ii) Thermal decomposition reaction. 
                            heat 
(iii) 2Pb(NO
3
)
2    
                  2PbO  + 4NO
2  
+  O
2 
 
0.5 + 0.5 
mark 
 
  1 mark         
  1 mark 
16 (i) Sodium bicarbonate/Sodium hydrogencarbonate/ baking soda and its formula is NaHCO
3
 
                            heat 
(ii)  2NaHCO
3
                     Na
2
CO
3 
+ CO
2 
+ H
2
O 
(iii) It is used in fire extinguisher and for baking. (any one) 
OR  
(i) Add 10 mL of concentrated sulphuric acid slowly to 90 mL of water with constant stirring. 
Dilution of acid is a highly exothermic process. If water is added to concentrated sulphuric acid, heat 
generated causes the mixture to splash leading to burns and the glass container can break.  
(ii) Decreases per unit volume. 
0.5 + 0.5 
mark 
1 mark 
1 mark 
 
1 mark 
1 mark 
1 mark 
17 Electronic configuration of     X: 2,8,2,    Y: 2,8,6 
Both X and Y belong to 3rd period. 
Ionic bond will be formed. 
Reason: X will lose 2 electrons and Y will gain 2 electrons to complete their octet and become stable. 
Formula is XY    
0.5 + 0.5 
mark 
0.5 mark 
1 mark 
0.5 mark 
18 A food chain showing Ist tropic level (½ mark), II
nd
 tropic level (½ mark), III
rd
 tropic level 
 (½ mark) and IV
th
 tropic level (½ mark). 
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted 
According to the 10% law, the amount of energy available will not be sufficient for the survival of the 
organism in the 5th trophic level. 
                                                               OR 
• Large jar filled with water, oxygen, food and aquatic plants and animals. 
• Oxygen/oxygen pump. 
• Fish food. 
• Aquatic plants/Producers provide O
2
 during photosynthesis. 
• Aquatic animals/Consumers release CO
2
 for the process of photosynthesis. 
• Decomposers are also important for natural cleaning of the aquarium. 
(0.5 mark for each point) 
2 mark 
 
 
1 mark 
 
 
 
 
 
 
3 mark 
3 
Central Board of Secondary Education 
 
19 
  
  
1+1+1 
mark 
 
 
 
 
20 Let purple trait be represented by: PP           White trait be : pp 
          parental          PP  X  pp 
                                          ? 
           F
1 
                  Pp X Pp    (Selfing) 
           F
2
 
                                         ? 
Gametes P p 
P PP Pp 
p Pp pp 
 
Visible characters of F1 progeny all flowers are purple coloured and in F2 progenies 3 are purple 
coloured and 1 is white coloured flower              
 
 
0.5 + 1 + 
0.5 mark 
 
 
 
 
 
0.5 + 0.5 
mark 
21 When growing plant shoot tip detects light a hormone called auxin is synthesised in the shoot tip which 
is sensitive to light. 
Auxin diffuses towards the shady side of the stem. 
It stimulates the growth of cells on the shady side of the plant which causes bending of the plant to the 
other side.  
This gives the appearance that the stem of the plant bends in the direction of light.  
1 mark 
0.5mark   
1 mark  
 
0.5 mark   
22 (i) Range of distance should be 0 cm to < 12 cm. 
(ii) The image will larger than the object. 
 
 (0.5 mark to be deducted if no arrows marked or wrongly marked arrows) 
(iii) Image will be at 24cm in front of the mirror or the image is formed at C 
0.5 mark 
 
 
 
1.5 mark 
 
 
 
 
 
1 mark 
4 
Central Board of Secondary Education 
 
23 
 
(i) Four components should be labelled. 
(ii) All of them should be in parallel and there should be a fuse for safety. 
(iii) Live and earth wires should be there. 
(0.5 mark to be deducted if all parts of the diagram are not labeled) 
 
 
 
 
 
 
 
 
 
1 mark 
0.5 + 0.5 
mark 
1 mark 
24 (i) The phenomenon is called dispersion. 
(ii) X — Violet     Y — Red  
(iii) Different colours of white light bend through different angles with respect to the incident beam of 
light due to difference in speed of light of different wavelengths.  
OR 
(i) Visible spectrum is the band of coloured components of a white light beam .  
(ii) Red light is scattered the least by air molecules and has longer wavelength. It travels the longest 
distance. 
(iii) The given setup will behave like a glass slab, resulting in recombination of the seven colours to 
produce white light. 
1 mark 
0.5 + 0.5 
mark 
1 mark 
 
1 mark 
1 mark 
 
1 mark 
 
SECTION C 
25 Metal X is Zinc 
The sulphide ore is first heated strongly in supply of oxygen and changed into its oxide. This process 
is called roasting. 
                         heat 
2ZnS  +  3O
2  
                 2ZnO + 2SO
2
 
 
Zinc oxide is then reduced to zinc metal by heating it with carbon. This process is called reduction. 
2ZnO +  C                   2Zn + CO
2
 
  
 
1 mark 
 
1 mark 
 
1 mark 
 
 
 
1 mark 
 
1 mark 
 
 
Page 5


1 
Central Board of Secondary Education 
 
CLASS X  
SCIENCE:  086 
 
Marking Scheme for Sample Question Paper 2019-20 
 
SECTION A 
1 The property of self-linking of atoms of an element through covalent bonds in order to form straight 
chain, branched chains or cyclic chains of different sizes is called catenation. 
1 mark 
2 The valency of an element first increases and then decreases across a period. 1 mark 
3(a) The principle behind electric generator is Electromagnetic Induction- the phenomenon of producing 
current in a coil by changing the magnetic field associated with it. 
1 mark 
3(b) The polarity of the output alternating current changes every 1/100 seconds. 
Alternately: 
In 1 second the output (AC) completes 50 cycles. 
1 mark 
3(c) 
The suitability of Muppandal as a site for wind farms stems from its geographical location as it has access 
to the seasonal monsoon winds.  
1 mark 
3(d) City A  
It is more suitable for a wind-farm as there is consistently high wind-speed in that city throughout the 
year.  
0.5 mark 
0.5 mark 
4(a) Diabetes 1 mark 
4(b) Insulin 1 mark 
4(c) iv) low sugar high fibre diet 1 mark 
4(d) i) 180mg/dL 1 mark 
5 ii) pupils take time to adjust 
OR 
ii) refraction 
1 mark 
6 ii) = 40  O. 
V=IR, V = 4V, I = 100 mA = 0.1 A 
Hence R = V/I = 4/0.1 O = 40  O.  
1 mark 
7 i) volt-ampere 
Power = Voltage x Current. 
1 mark 
8 iv) Human faecal matter 
OR 
iv) The Industralist 
1 mark 
9 iii) Carbon monoxide 1 mark 
10 iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. 1mark 
11 i) Na
2
CO
3
 1mark 
2 
Central Board of Secondary Education 
 
12 iii) C 
  OR 
iii) Q and R 
1mark 
13 i) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark 
14 iv) Assertion is false but reason is true. 1 mark 
 
SECTION B 
15 (i) It turns yellow due to formation of lead oxide and Reddish brown fumes evolve. 
(ii) Thermal decomposition reaction. 
                            heat 
(iii) 2Pb(NO
3
)
2    
                  2PbO  + 4NO
2  
+  O
2 
 
0.5 + 0.5 
mark 
 
  1 mark         
  1 mark 
16 (i) Sodium bicarbonate/Sodium hydrogencarbonate/ baking soda and its formula is NaHCO
3
 
                            heat 
(ii)  2NaHCO
3
                     Na
2
CO
3 
+ CO
2 
+ H
2
O 
(iii) It is used in fire extinguisher and for baking. (any one) 
OR  
(i) Add 10 mL of concentrated sulphuric acid slowly to 90 mL of water with constant stirring. 
Dilution of acid is a highly exothermic process. If water is added to concentrated sulphuric acid, heat 
generated causes the mixture to splash leading to burns and the glass container can break.  
(ii) Decreases per unit volume. 
0.5 + 0.5 
mark 
1 mark 
1 mark 
 
1 mark 
1 mark 
1 mark 
17 Electronic configuration of     X: 2,8,2,    Y: 2,8,6 
Both X and Y belong to 3rd period. 
Ionic bond will be formed. 
Reason: X will lose 2 electrons and Y will gain 2 electrons to complete their octet and become stable. 
Formula is XY    
0.5 + 0.5 
mark 
0.5 mark 
1 mark 
0.5 mark 
18 A food chain showing Ist tropic level (½ mark), II
nd
 tropic level (½ mark), III
rd
 tropic level 
 (½ mark) and IV
th
 tropic level (½ mark). 
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted 
According to the 10% law, the amount of energy available will not be sufficient for the survival of the 
organism in the 5th trophic level. 
                                                               OR 
• Large jar filled with water, oxygen, food and aquatic plants and animals. 
• Oxygen/oxygen pump. 
• Fish food. 
• Aquatic plants/Producers provide O
2
 during photosynthesis. 
• Aquatic animals/Consumers release CO
2
 for the process of photosynthesis. 
• Decomposers are also important for natural cleaning of the aquarium. 
(0.5 mark for each point) 
2 mark 
 
 
1 mark 
 
 
 
 
 
 
3 mark 
3 
Central Board of Secondary Education 
 
19 
  
  
1+1+1 
mark 
 
 
 
 
20 Let purple trait be represented by: PP           White trait be : pp 
          parental          PP  X  pp 
                                          ? 
           F
1 
                  Pp X Pp    (Selfing) 
           F
2
 
                                         ? 
Gametes P p 
P PP Pp 
p Pp pp 
 
Visible characters of F1 progeny all flowers are purple coloured and in F2 progenies 3 are purple 
coloured and 1 is white coloured flower              
 
 
0.5 + 1 + 
0.5 mark 
 
 
 
 
 
0.5 + 0.5 
mark 
21 When growing plant shoot tip detects light a hormone called auxin is synthesised in the shoot tip which 
is sensitive to light. 
Auxin diffuses towards the shady side of the stem. 
It stimulates the growth of cells on the shady side of the plant which causes bending of the plant to the 
other side.  
This gives the appearance that the stem of the plant bends in the direction of light.  
1 mark 
0.5mark   
1 mark  
 
0.5 mark   
22 (i) Range of distance should be 0 cm to < 12 cm. 
(ii) The image will larger than the object. 
 
 (0.5 mark to be deducted if no arrows marked or wrongly marked arrows) 
(iii) Image will be at 24cm in front of the mirror or the image is formed at C 
0.5 mark 
 
 
 
1.5 mark 
 
 
 
 
 
1 mark 
4 
Central Board of Secondary Education 
 
23 
 
(i) Four components should be labelled. 
(ii) All of them should be in parallel and there should be a fuse for safety. 
(iii) Live and earth wires should be there. 
(0.5 mark to be deducted if all parts of the diagram are not labeled) 
 
 
 
 
 
 
 
 
 
1 mark 
0.5 + 0.5 
mark 
1 mark 
24 (i) The phenomenon is called dispersion. 
(ii) X — Violet     Y — Red  
(iii) Different colours of white light bend through different angles with respect to the incident beam of 
light due to difference in speed of light of different wavelengths.  
OR 
(i) Visible spectrum is the band of coloured components of a white light beam .  
(ii) Red light is scattered the least by air molecules and has longer wavelength. It travels the longest 
distance. 
(iii) The given setup will behave like a glass slab, resulting in recombination of the seven colours to 
produce white light. 
1 mark 
0.5 + 0.5 
mark 
1 mark 
 
1 mark 
1 mark 
 
1 mark 
 
SECTION C 
25 Metal X is Zinc 
The sulphide ore is first heated strongly in supply of oxygen and changed into its oxide. This process 
is called roasting. 
                         heat 
2ZnS  +  3O
2  
                 2ZnO + 2SO
2
 
 
Zinc oxide is then reduced to zinc metal by heating it with carbon. This process is called reduction. 
2ZnO +  C                   2Zn + CO
2
 
  
 
1 mark 
 
1 mark 
 
1 mark 
 
 
 
1 mark 
 
1 mark 
 
 
5 
Central Board of Secondary Education 
 
OR 
(i) As it reacts with both acids as well as bases to form salts. 
(ii) Iron being more reactive than copper displaces copper from copper sulphate to form green 
ferrous sulphate solution. 
(iii) Nitric acid is a strong oxidising agent. Hydrogen gas produced gets oxidised to H
2
O. 
(iv) Calcium is a very reactive metal. It reacts with the chemicals in surroundings and occurs in 
combined state. 
(v) Sodium and potassium are highly reactive metals and react vigorously with oxygen in air and 
may even catch fire. They do not react with kerosene. 
 
 
   1 mark 
 
1 mark 
 
1 mark 
 
1 mark 
 
1 mark 
26 (i) D is a saturated hydrocarbon  
(ii) B is an organic acid.  
 
Structural formula  
 
 
 
(iii) C is the compound. 
 It acts as a dehydrating agent and removes a water molecule from ethanol. 
hot conc. H
2
SO
4
 
   C
2
H
5
OH                                           C
2
H
4
 + H
2
O 
 
(iv) 
                                             conc H
2
SO
4
 
CH
3
COOH  +  C
2
H
5
OH                                     CH
3
COOC
2
H
5
    + H
2
O   
Major product is Ester and it is used in making perfumes / flavouring agents. 
 
0.5  mark 
0.5  mark 
 
 
0.5 mark 
 
 
0.5 mark 
0.5 mark 
1 mark 
 
 
 
1 mark 
0.5  mark 
 
27 
 
(i) Oxygenated : B/D/F  [ B= left ventricle/D=aorta/F=left auricle/pulmonary vein] 
Deoxygenated: A/C/E [A= right ventricle/C= pulmonary artery/E=right auricle/vena cava]                                                                        
(any two) 
 
 
 
 
 
 
 
 
 
0.5 + 0.5 + 
0.5 +0.5 
mark