Calculate the molar mass of the following:
$(i)$ $H_2O$
$(ii)$ $CO_2$
$(iii)$ $CH_4$

$(i)$ Molar mass of water $(H_2O)$:
Atomic mass of $H = 1 \ u$,Atomic mass of $O = 16 \ u$
Molar mass of $H_2O = (2 \times 1) + (1 \times 16) = 18 \ g/mol$
$(ii)$ Molar mass of carbon dioxide $(CO_2)$:
Atomic mass of $C = 12 \ u$,Atomic mass of $O = 16 \ u$
Molar mass of $CO_2 = (1 \times 12) + (2 \times 16) = 44 \ g/mol$
$(iii)$ Molar mass of methane $(CH_4)$:
Atomic mass of $C = 12 \ u$,Atomic mass of $H = 1 \ u$
Molar mass of $CH_4 = (1 \times 12) + (4 \times 1) = 16 \ g/mol$