The number of neutrons in $5 \ g$ of $D_2O$ ($D$ is $_1^2H$) are ................ $N_A$.

What is the numerical value of $\frac{N}{n}$? (Where $N$ is the number of molecules in a given gas sample and $n$ is the number of moles of the gas.)

Find the number of molecules,number of carbon atoms,number of hydrogen atoms,and total number of atoms in $5.6 \ L$ of $CH_4$ at $STP$.

Calculate the number of molecules in $18 \ mg$ of water in terms of Avogadro's number $(N_A)$.

$6.02 \times 10^{20}$ molecules of urea are present in $200 \ mL$ of its solution. The concentration of urea solution is .............. $M$

What is the number of water molecules present in $1 \ mL$ of water?