a) When carbon dioxide is passed through the calcium hydroxide solution, it turns milky due to the formation of insoluble calcium carbonate.
b) Reaction in Test tube A:
\(\underset{Acetic\ or\ ethnoic\ acid}{2CH_3COOH(1)}+\underset{Sodium\ carbonate}{Na_2CO_3(s)}\rightarrow\underset{Sodium\ acetate}{2CH_3COONa}+\underset{Water}{H_2O}+\underset{Carbon\ ioxide}{CO_2(g)}\)
Reaction in Test tube B:
\(\underset{Calciumhydroxide\\ (Lime\ water)}{Ca(OH)_2(aq)}+\underset{Carbondioxide}{CO_2(g)}\rightarrow\underset{Calcium\ carbonate\\ (White\ ppt)}{CaCO_3(s)\downarrow}\underset{Water}{H_2O}\)
c) No with ethanol no reaction takes place.
d) When a quick lime i.e., calcium oxide is added to water in a test tube, it forms calcium hydroxide which is lime water. This solution is filtered and the clear solution is obtained
\(CaO(s)+H_2O(l)\rightarrow Ca(OH)_2\)

(a)  (i) The principal focus of a diverging lens is a point on its principal axis from which light rays, originally parallel to the axis appear to diverge after passing through the diverging (concave) lens. 
(ii) The distance between pole and principal focus of a diverging lens is called the focal length in the given diagram OF is the focal length.

(b) Divergent lens (Concave lens) Focal length, f = -30 cm 
Size of the object, h₁ = 6 cm 
Image distance, v = -15 cm 
Object distance, u = ? 
Size of the image, h₂ = ? 
According to the lens formula,
\(\frac { 1 }{ f } =\frac { 1 }{ v } +\frac { 1 }{ u } \)
\(\frac { 1 }{ -30 } =\frac { -1 }{ -15 } +\frac { 1 }{ u } \)
\(\Rightarrow \frac { 1 }{ u } =\frac { -1 }{ 15 } +\frac { 1 }{ 30 } =\frac { -2+1 }{ 30 } =\frac { -1 }{ 30 } \)
u=-30cm
\(\frac { { h }_{ 2 } }{ { h }_{ 1 } } =\frac { v }{ u } \)
\(\Rightarrow \frac { { h }_{ 2 } }{ 6 } =\frac { -15 }{ -30 } \)
\(\Rightarrow { h }_{ 2 }=\frac { 15 }{ 30 } \times 6=+3cm\)

(a) Mendel choose garden pea for his experiment because pea plants was self fertilising and have short life cycle.
(b) Mendel performed experiments on a garden pea (Pisumsativum) with different visible contrasting characters. He selected seven contrasting pairs of characters such as tall / short plants, purple / white flower colour etc.
(c) Mendel performed his experiment on tall and dwarf plant and interpreted his results to show that the traits may be dominant or recessive. Parent plants: True breeding tall pea plant was crossed with true breeding dwarf pea plant. Production of F₁ plants: All F₁ plants were found to be tall. Results of self-pollination ofF₁ plants or F₂plants: Mendel found that on self-pollination of F₁ plants, the progenies obtained in F₂ generations were not all tall plants. Instead, one- fourth of F₂plants were found to be dwarf.
Mendel's explanation for the reappearance of the short trait: From this experiment, Mendel concluded that the F₁ tall plants were not true breeding. They were carrying
both the traits. They appeared tall, because the tall trait was dominant over the dwarf trait.

DNA sequences are used for studying human evolution. There is no biological basis to the idea of human races. All human beings are a single species but there is a great diversity of human forms and features across the earth. The earliest members of human species Homo sapiens are traced from Africa.
The evidences in support are as follows:
1.Common body plan, structure, physiology and metabolism.
2.Constant chromosome number
3. Common genetic blue print
4. Free inter-breeding

A disease which can be transmitted through sexual contact is called sexually transmitted disease or STD. Lack of hygiene is usually a major factor in providing conditions for spread of STDs. But unprotected sex with multiple and unknown partners is the biggest reason for the spread of STDs. Some of the ways to prevents STDs are as follows
(a) Being faithful to one's life partner
(b) Avoiding sexual contact with unknown person.
(c) Using condom during sexual intercourse
(d) Maintain personal hygiene.

a) Compounds of carbon and hydrogen only are called hydrocarbons. For example
methane (CH₄), ethane (C₂H₆), ethene (C₂H₄), ethyne (C₂H₂), cydohexane
(C₆H₁₂), benzene (C₆H₆) etc.

b) Saturated hydrocarbons contains only C - C and C - H single covalent bonds while
unsaturated hydrocarbons contain at least one C = C double bond (besides C - C
and C - H single covalent bonds) or one triple bond.

c) That portion of the organic molecule which largely determine its chemical properties is called the functional group. For example, -OH (alcoholic group), (keto group) - CHO (aldehyde group), -COOH (carboxyl group).

(i) Concentrated sulphuric acid is called the king of chemicals as it is a very strong acid and is highly corrosive.
(ii) (a) When concentrated sulphuric acid acts on sulphur, sulphur dioxide gas is evolved.
        \(\underset { Suphur }{ S(s) } +\underset { Suphuricacid(conc.) }{ { 2H }_{ 2 }{ SO }_{ 4 }(I) } \underrightarrow { \Delta } \underset { Sulphurdioxide }{ { 3SO }_{ 2 }(g) } +\underset { Water }{ { 2H }_{ 2 }O(I) } \)
    (b) When dilute sulphuric acid acts on sodium carbonate, carbon dioxide gas is evolved.
         \(\underset { Sodiumcarbonate }{ { Na }_{ 2 }{ CO }_{ 3 }(g) } +\underset { Sulphuricacid }{ { H }_{ 2 }{ SO }_{ 4 }(aq) } \rightarrow \underset { Sodiumsulphate }{ { Na }_{ 2 }{ SO }_{ 4 }(aq) } +\underset { Carbondioxide }{ { CO }_{ 2 }(g) } +\underset { Water }{ { H }_{ 2 }O(I) } \)
(iii) (a) When concentrated sulphuric acid is added to blue copper sulphate crystals, white coloured anhydrous copper sulphate is formed.
        \(\underset { Copper(II)sulphatepentahydrate\\ \quad \quad (BlueCrystal) }{ { CuSO }_{ 4 }.{ 5H }_{ 2 }O } \overset { { conc.H }_{ 2 }{ SO }_{ 4 } }{ \underset { { -5H }_{ 2 }O }{ \longrightarrow } } \underset { Anhydrouscopper(II)sulphate\\ \quad \quad (Whitepowder) }{ { CuSO }_{ 4 } } \)
     (b) When concentrated sulphuric acid is added to colourless cane sugar crystals, it dehydrates sugar to a black mass of carbon known as sugar charcoal.
            \(\underset { Sugar\\ (White) }{ { C }_{ 12 }{ H }_{ 22 }{ O }_{ 11 } } \overset { { conc.H }_{ 2 }{ SO }_{ 4 } }{ \underset { { -11H }_{ 2 }O }{ \longrightarrow } } \underset { Carbon\\ (Black) }{ 12C } \)

Since the non-metal A is the largest costituent of air, it must be Nitrogen. When nitrogen is heated with hydrogen in the ratio of 1 : 3, it gives ammonia in presence of iron as a catalyst [Haber's process]. When nitrogen is heated with oxygen, it gives nitric oxide. When this oxide is passed through water in presence of air, it gives nitric acid which acts as a strong oxidising agent.
(a) A - N₂; B - NH₃; C - NO; D - HNO₃
(b) Element A belongs to Group - 15 of the Periodic Table.

The mechanism of exchange of gases takes place between the blood and body tissues during respiration. The air enters the lungs through nostrils. As the blood passes
through the body tissues, the oxygen present in it diffuses into the cells due to its higher concentration in the blood. A red pigment called haemoglobin in the blood carries the oxygen. This oxygen combines with the digested food to release energy, which takes place in mitochondria of the cells. The carbon dioxide produced during the respiration diffuses into the blood stream from where it is carried to lungs and expelled out. The blood which comes from the lungs has a higher concentration of oxygen but the body tissues have a higher concentration of carbon dioxide. Due to the difference in the concentrations, the exchange of gases between the blood and the body tissues takes place. Thus, in this way the process of gaseous exchange is completed in the human respiratory system. The total area for gaseous exchange provided by 300 million alveoli in 2 IU,ngsis 400-800 square feet.

A solenoid behaves like a magnet when electric current flows through it. Any current carrying conductor creates a magnetic field around it. For determining the different poles of a solenoid, we can use a bar magnet and look for interaction between different poles of a solenoid, we can use a bar magnet and look for interaction between different poles of two magnets. If the north pole of the bar magnet gets repulsed by a particular pole of the electromagnet (solenoid) then it gets confirmed that the bar by a particular pole of the electromagnet (solenoid) then it gets confirmed that the bar magnet was brought near the north pole of the electromagnet. 

Reflex action is a special case of involuntary movement involuntary organs. When a voluntary organ is in the vicinity of a sudden danger, it is immediately pulled away from the danger to save itself. For example; when your hand touches a very hot electric iron, you move away your hand in a jerk. All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.
Reflex Arc: The path through which nerves signals; involved in a reflex action; travel is called the reflex arc. The following flow chart shows the flow of signal in a reflex arc. Receptor \(\rightarrow\) Sensory Neuron\(\rightarrow\) Relayneuron \(\rightarrow\) Motor neuron \(\rightarrow\) Effector (muscle) The receptor is the organ which comes in the danger zone. The sensory neurons pick signals from the receptor and send them to the relay neuron. The relay neuron is present in the spinal cord. The spinal cord sends signals to the effector via the motor neuron. The effector comes in action moves the receptor away from the danger.

(a) Baking soda is sodium hydrogen carbonate.  On heating, it is converted carbonate.  On heating, it is converted into sodium carbonate which is bitter to taste.

\(2NaHCO_3\xrightarrow{Heat}Na_2CO_3+H_2O+CO_2\)

(b) Baking soda can be converted into baking powder by the addition of appropriate acid to it.

(c) The role of tartaric acid is to neutralise sodium carbonate and cake will not taste bitter.

(a) The element A which is a yellow solid at room temperature and shows catenation and allotropy is sulphur (S).
(b) The atomic number of sulphur is 16. Therefore, its electronic configuration is 2, 8, 6.
(c) \(\underset { Ferroussulphate }{ { 2FeSO }_{ 4 } } \underrightarrow { Heat } \underset { Ferricoxide }{ { Fe }_{ 2 }{ O }_{ 3 } } +\underset { Sulphurdioxide }{ { SO }_{ 2 } } +\underset { Sulphurtrioxide }{ { SO }_{ 3 } } \)
    Both SO₂ and SO₃ are major air pollutions.
(d) Since sulphur is a non-metal, therefore both S02 and S03 are acidic oxide since they dissolve in water to form the corresponding acids.
        \(\underset { Sulphurdioxide }{ { SO }_{ 2 } } +\underset { Water }{ { H }_{ 2 }O } \rightarrow \underset { Sulphurousacid }{ { H }_{ 2 }{ SO }_{ 3 } } \\ \underset { Ferroustrioxide }{ { SO }_{ 3 } } +\underset { Water }{ { H }_{ 2 }O } \rightarrow \underset { Sulphuricacid }{ { H }_{ 2 }{ SO }_{ 4 } } \)
(e) Since sulphur contains six valence electrons, therefore it lies in group 6 + 10 = 16.Further, since atomic number of sulphur (S) is 16. It lies in the 3rd period.

Atomic number of Calcium is 20 and its electronic configuration is 2, 8, 8, 2. To see the resemblance with Calcium, first we have to check the Electronic Configuration of respective elements.

From above, it is clear, elements with atomic number 12 and 38 has same electronic configuration of valence shell as that of Calcium, and therefore, will have physical and chemical properties resembling calcium.

(a) The properties of all elements in the boron family
      (i) All the elements show valency of 3.
(b) The properties of  all the elements in halogen family
    (i) All the elements possess seven electrons in the valence shell.