Total number of atoms represented by the compound $CuSO_4 \cdot 5H_2O$ is

If $10^{21}$ molecules are removed from $200 \ mg$ of $CO_2$,how many moles of $CO_2$ will remain?

The mass of $10^{21}$ atoms of $Cu$ is ..... grams.

$2.8 \times 10^{-3} \ mol$ of $CO_2$ is left after removing $10^{21}$ molecules from its '$x$' $mg$ sample. The mass of $CO_2$ taken initially is. Given: $N_A = 6.02 \times 10^{23} \ mol^{-1}$. (in $mg$)

$A$ $500 \, mL$ solution of $NaOH$ contains $3.01 \times 10^{22}$ molecules of $NaOH$. What is the molarity $(M)$ of the $NaOH$ solution?

Which one of the following pairs of gases contains the same number of molecules?