Answer: It has very high calorific value and burns cleanly.
- A It has very high calorific value and burns cleanly
- B It is currently the cheapest fuel available on the market
- C It exists as a stable solid at room temperature
- D It is classified as a non-flammable gas
Correct answer: A. It has very high calorific value and burns cleanly
Explanation: Hydrogen has the highest energy density per unit mass and produces only water on combustion.
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.