a) Nickel (Ni) is a catalyst which adsorbs hydrogen molecule on its surface and then with alkenes molecule side by side. The two hydrogen atom then is added to form an addition product.
b) The presence of concentrated sulphuric acid increases the rate of forward reaction by removing water formed during the reaction.
c) Alkaline potassium permanganate act as mild oxidizing agent and so convert ethanol to ethanoic acid.

\(P=\frac { 1 }{ f } \)
For obtaining more convergent light, power of lens must be larger. Therefore, its focal length must be smaller. Therefore, the lens of f = 20 cm will provide more convergent light.

(a) A male individual contains one X chromosome and one Y chromosome. So male produces two different kinds of. gametes.  Therefore, male are called heterogametic. A female individual contains two similar X chromosomes. So produces only one kind of gamete. Therefore, female are called homogametic. The sex of the child is determined at the time of fertilization when male and female gametes fuse to form zygote. If a sperm carrying X chromosome fertilizes an egg carrying X chromosome, then the offspring will be a female, because the offspring will have XX chromosomes. If a sperm carrying Y chromosome fertilizes an egg carrying X chromosome, then the offspring will be a male, because the offspring will have XY chromosomes. Thus there is 50% chance of a male child being born and a 50% chance of a female child being born. Thus, it is the sperm which determines the sex of the child.
(b) In some reptiles, the temperature at which the fertilised  egg is incubated before hatching plays a role in determining the sex of the offspring. Example: In a turtle, high
incubation temperature leads to female offspring.

Hydrogen occupies a unique position in the modern periodic table because of the following reasons:
(i) Both hydrogen and halogens have similar outer electric configuration. Therefore some of the properties of hydrogen are similar to those of alkali metals and hence it can be placed in group 1 along with alkali metals.
(ii) Both hydrogen and halogens have similar outer electric configuration. Therefore some of the properties of hydrogen are similar to those of halogens and hence it can be placed in group 17 along with halogens.
(iii) In some properties, it differs from both hydrogen and halogens. For examples, the oxide of hydrogen (H ₂O) is neutral but the oxides of alkali metals (Na ₂O, K₂O) are basic while those of halogen (Cl₂O₇, Br₂O₅) are acidic.

The answer to the first part of this question is a definite yes. Meiosis is the cell division which happens during gametogenesis, i.e. during gamete formation. This results in number of chromosomes getting halved in gametes. When fertilization happens, the number of chromosomes becomes equal to that in somatic cells. After that, mitosis takes place during rest of the stages of life. And thus, the constancy of chromosomal number is maintained in all the three stages as mentioned in this question.

Both carbon and silicon have  similar valence shell electronic configuration that is each has four electrons in the valence shell and hence show the phenomenon of catenation. But carbon being smaller than silicon forms stronger c-C than Si-Si bonds. Thus due to greater strength of C-C over Si-Si bonds, carbon shows catenation to a greater extent than silicon.

Fe is more reactive as compared to Cu. Therefore, Fe displaces Cu from CuSO₄ and forms FeSO₄.
\(Fe+{ CuSO }_{ 4 }\rightarrow { FeSO }_{ 4 }+Cu\)

The earth wire is connected to a metallic plate buried deep inside the earth. In this way, the metallic body of appliance is connected to the earth, which provides a low resistance conducting path for electric current. Hence, any leakage of current to the metallic body of appliance flows to the earth through the earth wire. The user might not get a severe electric shock on touching such an appliance in case of a fault.

(a) A is carbon, B is carbon monoxide and C is carbon dioxide.
(b) A belongs to Group - 14 of the Periodic Table.

Guard cells control the opening and closing of stomatal pore by change in turgidity. When water enters the guard cells, they become turgid and the stomatal pore opens. On the other hand, when water exits from the guard cells; they become flaccid and the stomatal pore opens.

(a) Anode       : Impure silver;
     Cathode     : Pure silver
(b) Electrolyte : Silver salt, such as AgNO₃
(c) We get pure silver at cathode.

(a) Oestrogen
(b) Growth hormone
(c) Insulin
(d) Thyroxine

(i) Alkaline medium does not allow milk to turn sour easily.
(ii) When milk is set to curd, the presence of alkali does not allow it to become acidic easily. Hence, this milk take a longer time to set as a curd.