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

$N a \left(s\right) + {H}_{2} O \left(l\right) \rightarrow N a O H \left(a q\right) + {H}_{2} \left(g\right)$
Unless you specify from what reagent the gas was formed we cannot help you. Note that $250 \cdot g$ is a very large molar quantity of dihydrogen gas, and it would occupy a lot of volume under standard conditions.