Answer: Its H–H bond enthalpy is very high.
- A It spontaneously ionises to give H<sup>+</sup>
- B Its molecules are strongly polar
- C It has a very high electron affinity
- D Its H–H bond enthalpy is very high
Correct answer: D. Its H–H bond enthalpy is very high
Explanation: The strong H–H bond (about 435.9 kJ mol<sup>-1</sup>) must be broken for a reaction, so dihydrogen is comparatively inert unless heated or a catalyst is used.
Each water molecule's O-H bonds (covalent, solid) can hydrogen-bond (dashed) to neighbouring molecules, forming an extended network responsible for water's unusually high boiling point and density anomaly.
Concept context
The simplest and most abundant element in the universe. Study its unique position in the periodic table, isotopes (protium, deuterium, tritium), properties of water and hydrogen peroxide, and industrial uses.