Calculate the mass of $0.25 \ mol$ of iron (molar mass $= 56 \ g \ mol^{-1}$).

The number of molecules of $CO_2$ present in $44 \ g$ of $CO_2$ is

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

If $N_A$ is Avogadro’s number,then the number of valence electrons in $4.2 \ g$ of nitride ions $(N^{3 -})$ is ................... $N_A$.

If the market prices of table salt $(NaCl)$ and table sugar $(C_{12}H_{22}O_{11})$ are $Rs. 4$ per $kg$ and $Rs. 30$ per $kg$ respectively,then the market price of $1$ mole of each will be,respectively,..... $Rs$.

The number of molecules in $16 \ g$ of methane is ...... $\times 10^{23}$.