total no. of neutrons present in 4gof heavy water (D₂O) is?

$$\begin{gathered} Noofmoles=\frac{Givenmassing}{molarmass} \\ =\frac{4}{20}=0.05mole \\ Noofmolecules=mole\times Avogadronumber \\ =0.05\times 6.022\times {10}^{23} \\ =0.3011\times {10}^{23} \\ Noofneutronsinonemoleculeof{D}_{2}O=(2\times 1+8)=10 \\ Noofneutronsin0.3011\times {10}^{23}of{D}_{2}O=0.3011\times {10}^{23}\times 10 \\ =3.011\times {10}^{23} \end{gathered}$$