C2H2\mathrm{C}_{2} \mathrm{H}_{2}C2H2
C2H4\mathrm{C}_{2} \mathrm{H}_{4}C2H4
NH3\mathrm{NH}_{3}NH3
H2 S\mathrm{H}_{2} \mathrm{~S}H2 S