The lone pair of electrons can be identified by drawing structure of the given moleules as follows,

The number of molecules having only $2$ lone pair of electrons $= 3$

Which are ${\mathrm{H}}_2\mathrm{O},{\mathrm{N}}_2$ and $\mathrm{CO}$. ${\mathrm{XeF}}_4$ have $2$ lone pairs on central atom, but we are asked about lone pair in molecule