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

$(i)$ $1 \ mol$ of ethane $(C_2H_6)$ contains $2 \ mol$ of carbon atoms. Therefore,$3 \ mol$ of ethane contains $3 \times 2 = 6 \ mol$ of carbon atoms.
$(ii)$ $1 \ mol$ of ethane $(C_2H_6)$ contains $6 \ mol$ of hydrogen atoms. Therefore,$3 \ mol$ of ethane contains $3 \times 6 = 18 \ mol$ of hydrogen atoms.
$(iii)$ $1 \ mol$ of ethane contains $6.022 \times 10^{23}$ molecules. Therefore,$3 \ mol$ of ethane contains $3 \times 6.022 \times 10^{23} = 18.066 \times 10^{23}$ molecules of ethane.