The number of atoms in $8 \ g$ of sodium is $x \times 10^{23}$. The value of $x$ is ...... (Nearest integer).
$[ \text{Given}: N_{A} = 6.02 \times 10^{23} \ mol^{-1}, \text{Atomic mass of } Na = 23.0 \ u ]$

In a sample of $CaCO_3$,there are $3.01 \times 10^{23}$ ions of $Ca^{+2}$ and an equal number of $CO_3^{-2}$ ions. The mass of the sample is = $......$ grams.

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 $STP$.

What is the number of molecules in $4.25 \ g$ of $NH_3$?

The number of moles in $620 \ g$ of sodium oxide is ..... moles.

Natural abundances of $^{12}C$ and $^{13}C$ isotopes of carbon are $99\,\%$ and $1\,\%$,respectively. Assuming they only contribute to the molecular weight of $C_2F_4$,the percentage of $C_2F_4$ having a molecular mass of $101$ is $.....$