$\mathrm{g}.$at. wt. of $\mathrm{N}=14 \mathrm{g};$

Avogadro no.$= 6.023\times {10}^{23}$ 

We know that:  

$\mathrm{g}.$ at. wt. of $\mathrm{N} =$ Wt. of one atom of N in $\mathrm{amu}\times 1.66 \mathrm{x} {10}^{- 24} \mathrm{g} \times$ Avogadro no. $(= 6.023 \mathrm{X} 10 23 )$

$14 \mathrm{g}$ =Wt. of one atom of N in $\mathrm{amu} \times 1.66\times {10}^{- 24 }\mathrm{g} \times 6.023\times {10}^{23}$

$\therefore$Wt. of one atom of $\mathrm{N}$ in $\mathrm{amu}$

$=\frac{14\mathrm{g}}{1.66\times {10}^{-24}\mathrm{g}\times 6.023\times {10}^{23}}$

$=14 \mathrm{amu}$