Statement (A): One mole of sodium ions $\left({\mathrm{Na}}^{+}\right)$ containing $6.023\times {10}^{23} {\mathrm{Na}}^{+ } \mathrm{ions}$

Statement (B): Atomic mass of chlorine is 35.5 a.m.u

Statement (C): The units of vapour density are gm/c.c.

Vapour density has no units because it is a relative quantity. Density of any compound compare with density of hydrogen gas. 

$\mathrm{Vapor} \mathrm{density} (\mathrm{V}.\mathrm{D}) =\frac{\mathrm{density} \mathrm{of} \mathrm{compounds} (\mathrm{gm}/\mathrm{cc})}{\mathrm{density} \mathrm{of} \mathrm{hydrogen} (\mathrm{gm}/\mathrm{cc})}= \mathrm{no} \mathrm{units}$