State one appropriate observation for :

(i) Copper sulphide is treated with dilute hydrochloric acid.

(ii) A few drops of dil. HCl are added to AgNO₃ soln. followed by addition of NH₄OH soln.

State your observation:
Dilute HCl is added to sodium carbonate crystals.

Fill in the blank from the choices in the bracket :

Quicklime is not used to dry HCl gas because …………… [CaO is alkaline, CaO is acidic, CaO is neutral]

Study the figure given below and answer the questions that follow :

(i) Identify the gas Y.

(ii) What property of gas Y does this experiment demonstrate?

(iii) Name another gas which has the same property and can be demonstrated through this experiment.