What is meant by order of a reaction?

The kinetics of a reaction. $\mathrm{A}+2 \mathrm{B}⟶\mathrm{C}+\mathrm{D}$ obey the rate equation, rate $=\mathrm{k}{\left[\mathrm{A}\right]}^{\mathrm{x}}{\left[\mathrm{B}\right]}^{\mathrm{y}}$. For it find out: order of reaction.

The kinetics of a reaction. $\mathrm{A}+2 \mathrm{B}⟶\mathrm{C}+\mathrm{D}$ obey the rate equation, rate $=\mathrm{k}{\left[\mathrm{A}\right]}^{\mathrm{x}}{\left[\mathrm{B}\right]}^{\mathrm{y}}.$ For it find out: apparent molecularity of reaction.

The kinetics of a reaction. $\mathrm{A}+2 \mathrm{B}⟶\mathrm{C}+\mathrm{D}$ obey the rate equation, rate $=\mathrm{k}{\left[\mathrm{A}\right]}^{\mathrm{x}}{\left[\mathrm{B}\right]}^{\mathrm{y}}$. For it find out: order of reaction when $\mathrm{B}$ is present in large excess.

Nitric oxide reacts with hydrogen to give nitrogen and water: $2\mathrm{NO}+2{\mathrm{H}}_2⟶{\mathrm{N}}_2+2{\mathrm{H}}_2\mathrm{O}$.

The kinetics of this reaction is explained by the following steps:

$$\begin{gathered} \left(\mathrm{i}\right) 2\mathrm{NO}+{\mathrm{H}}_2⟶{\mathrm{N}}_2+{\mathrm{H}}_2{\mathrm{O}}_2 \left(\mathrm{slow}\right). \\ \left(\mathrm{ii}\right) {\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{H}}_2\to 2{\mathrm{H}}_2\mathrm{O} \left(\mathrm{fast}\right). \end{gathered}$$

What is the predicted rate law?