Question

What reaction has occurred when a `250*g` mass of dihydrogen gas is a product?

Answer 1

What was the reaction?

Explanation:

Dihydrogen gas could be a product of alkali metal reduction:

`Na(s) + H_2O(l) rarr NaOH(aq) + H_2(g)`

Unless you specify from what reagent the gas was formed we cannot help you. Note that `250*g` is a very large molar quantity of dihydrogen gas, and it would occupy a lot of volume under standard conditions.