$6.02 \times 10^{20}$ molecules of urea are present in $200 \ mL$ of its solution. The concentration of urea solution is .............. $M$

Calculate the following for $3 \ mol$ of ethane $(C_2H_6)$:
$(i)$ Number of moles of carbon atoms
$(ii)$ Number of moles of hydrogen atoms
$(iii)$ Number of molecules of ethane

If a gaseous mixture contains $20\%$ $H_2$ by weight,what is the number of moles of $H_2$ in $100 \ g$ of the mixture (in $mol$)?

The maximum number of molecules is present in

What is the number of $CO_2$ molecules in $45.42 \ L$ at $\text{STP}$? (Consider molar volume of gas at $\text{STP} = 22.71 \ L \ mol^{-1}$)

The number of molecules in $16 \ g$ of methane is