From $392 \, mg$ of $H_2SO_4$,$1.204 \times 10^{21}$ molecules are removed. How many moles of $H_2SO_4$ are left?

Find the number of hydrogen atoms present in $6.0 \ g$ of urea $(NH_2CONH_2)$:

If $10^{21}$ molecules are removed from $200 \ mg$ of $CO_2$,then the number of moles of $CO_2$ left are .......... $\times 10^{-3}$.

If it takes $1$ second to count $4$ grains of wheat,then the time required to count one mole of wheat grains is ...... years.

The ratio of the number of oxygen atoms $(O)$ in $16.0 \ g$ ozone $(O_3)$,$28.0 \ g$ carbon monoxide $(CO)$,and $16.0 \ g$ oxygen $(O_2)$ is (Atomic mass: $C = 12$,$O = 16$ and Avogadro's constant $N_A = 6.0 \times 10^{23} \ mol^{-1}$)

Which of the following figures does not represent $1 \ mole$ of $O_2$ gas at $NTP$?