Question

state a method to prove that the gas jar used for collection of HCL gas is filled with HCl​

Answer 1

We can use moist blue litmus paper to check so as due to the presence of HCl the blue litmis will turn red.

Answer 2

In order to know that the jar is filled with the gas, bring a glass rod dipped in ammonium hydroxide solution near its mouth. If dense white fumes of ammonium chloride are produced, it indicates that the gas jar is full of HCl gas.