A gas 'A' reacts with another gas 'B' in the presence of a catalyst to give a colourless gas 'C'. The gas 'C' when comes in contact with air produces a brown gas 'D'. The solution of 'A' in water turns red litmus blue. Explain the observations.

(i) Name the common refrigerant. How does it deplete ozone layer?

(ii) What is the alternative of chlorofluorocarbon carbon?

(iii) State the advantages and disadvantages of using ammonia as refrigerant?

(a) Of the two gases, ammonia and hydrogen chloride, which is more dense? Name the method of collection of this gas.

(b) Give one example of a reaction between the above two gases which produces a solid compound.

Study the flow chart given and give balanced equations to represent the reactions A, B and C.

$\text{Mg}$3\text{N}2 \xrightarrow{\text{A}} \text{NH}3 \xtofrom[\text{C}]{\text{B}} \text{NH}4\text{Cl}