Chapter-chemical reactions and equations -

How can we test for the presence of hydrogen gas?

During any chemical reaction just cover the vessel in which you re doing the experiment with cork and put a glass tube through it so that half of the glass is inside and other half is outside now after reaction or at its end point take a matchstick   put it over the glass tube so that gases coming from tube came in contact with it. if the matchstick ignites with pop sound then it shows the presence of hydrogen gas. 

If the required gas is hydrogen gas then it burn with a popping  sound when kept in

contact with fire.Hence if the gas burns with a popping sound , then it is HYDROGEN GAS