Find how many L of hydrogen gas are formed at STP if 30 g of Zn reacts with hydrogen.

The information you have provided is incorrect. When zinc
reacts with hydrogen, hydrogen is not produced. Hydrogen is already
there, it cannot be produced during the reaction.

Instead
the reaction may lead to the formation of zinc hydride or
ZnH2.

Though this is not the usual way in which ZnH2 is
produced. Reactions such as

2LiH + ZnBr2 → ZnH2 +
2LiBr

2NaH + ZnI2 → ZnH2 +
2NaI

among many others are more widely used to produce zinc
hydride.

If this is not what you require, you would have to
present the question in a more accurate way for a proper answer.