Question

state one condition under which chlorine and hydrogen react to form hydrogen chloride gas

Answer 1

when hydrogen is in gas and chlorine is in liquid then they combine to form hydrogen chloride gas.you shold heat h2 and cl2 to form 2hcl.

Answer 2

Here the combination reaction takes place.

Here ,

Hydrogen + Chlorine → Hydrogen Chloride

We can write it in the equation form and a balanced equation too.

H + Cl → 2HCl

Here the hydrogen gas combined with chlorine and it forms Hydrogen Chloride.