If $100 \ mL$ of a urea solution contains $6.022 \times 10^{20}$ molecules,what is the concentration of the urea solution in $M$?

In $3$ moles of ethane $(C_{2}H_{6})$,calculate the following:
$i.$ Number of moles of carbon atoms.
$ii.$ Number of moles of hydrogen atoms.
$iii.$ Number of molecules of ethane.

How many water molecules are there in one drop of water $($Volume $= 0.0018 \ mL)$ at room temperature?

$10 \ dm^3$ of $N_2$ gas and $10 \ dm^3$ of gas $X$ at the same temperature and pressure contain the same number of molecules. The gas $X$ is

The ratio of masses of oxygen and nitrogen in a particular gaseous mixture is $1 : 4$. The ratio of the number of their molecules is:

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