The correct option is D H2S
H2S have lowest boiling point. since we know that liquids have more boiling point than gases. Here H2O is liquid so it will have higher boiling point than others. Out of Cl2, NH3 and H2S, Cl2 has more Boiling point due to its high molecular weight. Now out of NH3 and H2S, NH3 has higher boiling point due to the presence of stronger hydrogen bonding.