Question

Help with this question please.

Answer 1

There are 4 hydrogens on the right side $(2\mathrm H_2=4\mathrm H)$, and 2 hydrogens on the left per molecule of $\mathrm H_2$. To get the same number of hydrogens on both sides, the coefficient should be 2.

(Then the number of oxygens will be consistent, since $2\mathrm H_2\mathrm O$ contributes 2 oxygens, and so does $\mathrm O_2$.)