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

Which of the following has the maximum number of molecules?

The number of $Cl^{-}$ ions in $333 \ g$ of anhydrous $CaCl_2$ will be ................ $N_A$.

Calculate the number of $Ca^{2+}$ ions in $222 \ g$ of anhydrous calcium chloride $(CaCl_2)$? (Atomic mass: $Ca = 40 \ u$,$Cl = 35.5 \ u$)

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

The number of oxygen atoms in $4.4 \ g$ of $CO_2$ is approximately: