What is the “molecularity” of a reaction? How is it different from the order of reaction? Name one bimolecular and trimlecular gaseous reaction

The number of atoms or ions or molecules are taking part in an elementary reaction which must colloid simultaneously to bring about a chemical reaction is known as molecularity.
Eg:
${\mathrm{NH}}_4{\mathrm{NO}}_2\to {\mathrm{N}}_2+2{\mathrm{H}}_2\mathrm{O} (\mathrm{uni} \mathrm{molecular})$
$2\mathrm{HI}\to {\mathrm{H}}_2+{\mathrm{I}}_2$ (bi molecular)
$2\mathrm{NO}+{\mathrm{O}}_2\to 2{\mathrm{NO}}_2$ (tri molecular)
Sum of the powers of concentration of reactants in the rate equation is known as order of reaction.
Eg: $\mathrm{r}=\mathrm{K}\left[\mathrm{A}{]}^1\right[\mathrm{B}{]}^2$
Order : 1+ 2 = 3
1. Order maybe 0, but molecularity cannot be zero.
2. Order of reaction calculated experimentally but molecularity is calculated by mechanism of reaction
3. Order is applicable to elementary as well as complex reactions molecularity is applicable only for elementary reaction.