What happens when hydrogen burns in air?

In a flame of pure hydrogen gas, burning in air, the hydrogen $\left(H_2\right)$ reacts with oxygen $\left(O_2\right)$ to form water $\left(H_{2}O\right)$ and releases heat.

If carried out in atmospheric air instead of pure oxygen (as is usually the case), hydrogen combustion may yield small amounts of nitrogen oxides, along with the water vapor.