How many moles of urea are present in $5.4 \ g$? (Molar mass $= 60 \ g/mol$)

The number of oxygen atoms in $4.4 \ g$ of $CO_2$ is approximately ........ $\times 10^{23}$.

Which one of the following statements is incorrect?

The number of gram molecules of chlorine in $6.02 \times 10^{25}$ hydrogen chloride molecules is

The number of hydrogen atoms present in $5.4 \ g$ of urea is : (Given : Molar mass of urea: $60 \ g \ mol^{-1}$, $N_{A} = 6.022 \times 10^{23} \ particles \ mol^{-1}$)

At the same temperature,$10 \ dm^3$ of $N_2$ gas and $10 \ dm^3$ of gas $x$ contain the same number of molecules. What is the gas $x$?