What is the answer for it

Dear student, 
1. Upward displacement of air means collection of a gas below air i.e. by displacing air upwards.
Set up for the production of HCl gas is as follows:

When NaCl (common salt) is reacted with sulphuric acid, HCl gas is produced which is collected in the gas jar by upward displacement of air.
2.HCl gas is collected by the upward displacement of air as it is heavier than air and not water.
HCl is highly soluble in water as a result it forms hydrochloric acid when dissolved in water. 
Regards