What is the weight in $g$ of $2.01 \times 10^{23}$ molecules of $CO$?

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

The highest number of helium atoms is in

$4.4 \ g$ of $CO_2$ and $2.24 \ L$ of $H_2$ at $\text{STP}$ are mixed in a container. The total number of molecules present in the container will be :

The mass of $0.1 \ mol$ of methane $(CH_4)$ is ...... $g$.

$6.02 \times 10^{20}$ molecules of urea are present in $100 \ mL$ of its solution. The concentration of urea solution is ......... $M$.