How many isotopes of Hydrogen are there? Give their names.

Hydrogen does not combine with

The reaction of $H_2S$ with $O_2$ produces .....

When steam is passed over red hot iron,the substances formed are

Lithium hydride can be used to prepare other useful hydrides. Beryllium hydride is one of them. Suggest a route for the preparation of beryllium hydride starting from lithium hydride. Write chemical equations involved in the process.

What do you understand by the terms: $(i)$ hydrogen economy,$(ii)$ hydrogenation,$(iii)$ syngas,$(iv)$ water-gas shift reaction,and $(v)$ fuel-cell?