Zinc + Hydrochloric Acid - Zinc Chloride and Hydrogen Gas Zn + 2HCI - ZnCl2 + Hz
I know there are 2 atoms of hydrogen in the products because there is

O a 2 in front of hydrochloric acid
O a 2 behind HCI
O a 2 behind H

O a 2 in front of hydrochloric acid

Explanation:

the given reaction is :-

=》Zn + 2 HCL -> ZnCl2 + H2

since, mass can't be created or destroy, so number of hydrogen atoms in the reaction should be equal in product as in reaction.

so, there is 2 hydrogen in product hence there are two hydrogen in the reactants also.

it is showed in the reaction by putting a 2 in front of hydrochloric acid ( HCl ).