Answer: Helium, the noble gas with two protons and two neutrons in its common isotope.
- A Helium, the noble gas with two protons and two neutrons in its common isotope
- B Protium, the most abundant isotope with one proton and no neutrons in standard practice
- C Deuterium, the isotope with one proton and one neutron under most conditions encountered
- D Tritium, the radioactive isotope with one proton and two neutrons as frequently observed in practice
Correct answer: A. Helium, the noble gas with two protons and two neutrons in its common isotope
Explanation: Helium (He) is a separate element. The three isotopes of hydrogen are protium (H), deuterium (D), and tritium (T).
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.