Which has highest boiling point

Answer: H₂O has the highest boiling point among H₂O, H₂S, H₂Se, and H₂Te.

Boiling point order:
H₂S < H₂Se < H₂Te < H₂O

Why H₂O boils much higher: An Explanation

The boiling point of a substance depends on the strength of intermolecular forces (IMFs) holding its molecules together in the liquid phase. Stronger IMFs require more thermal energy to overcome, leading to higher boiling points.

Across the group 16 hydrides (H₂S, H₂Se, H₂Te), boiling point generally increases down the group. This happens because heavier atoms (S → Se → Te) have larger electron clouds that are more polarizable, strengthening London dispersion forces. That’s why H₂Te boils higher than H₂Se, which boils higher than H₂S.

However, water (H₂O) is a major exception to this trend. Oxygen is highly electronegative and small, allowing water molecules to form strong, directional hydrogen bonds which is a special type of intermolecular attraction far stronger than dispersion forces. Each H₂O molecule can form up to four hydrogen bonds in a 3D network, dramatically increasing cohesion in the liquid. As a result, far more heat is required to separate water molecules into vapor, giving H₂O a boiling point of 100 °C—much higher than H₂Te (~−2 °C), H₂Se (~−41 °C), or H₂S (~−60 °C).