Question

what happens when ammonia comes in contact with hydrogen chloride gas. ​

Answer 1

$holaa.....$
A white solid fume of NH4CL is obtained. 
It can be a test for th presence of ammonia. 
NH3 (g) + HCl (g) ->NH4CL (s)
hope it helps.:)

Answer 2

it performs a chemical reaction i.e.
NH3+HCl --› NH4Cl +H2
please mark it as the brainliest answer