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H₂O boils at 100°C but H₂S at −60°C, though S is heavier. Explain. Step 1: Both are bent molecules with similar structures. Step 2: H₂O forms strong H-bonds (O is small, very electronegative). Step 3: H₂S cannot H-bond effectively (S larger, less electronegative). Step 4: Extra energy needed to break H₂O's H-bond network → much higher bp. Same reason: HF liquid at 19.5°C, HCl gas at −85°C.