Science (086) — AI-generated practice question

Hydrogen (H₂ — single bond):
Hydrogen has only 1 valence electron. It needs just 1 more electron to complete its duplet (stable configuration of 2 electrons). So each hydrogen atom shares one electron with the other, forming a single bond (one shared pair), and both atoms achieve a duplet.

Oxygen (O₂ — double bond):
Oxygen has 6 valence electrons. It needs 2 more electrons to complete its octet (stable configuration of 8 electrons). Sharing just one pair would leave each oxygen atom with only 7 electrons — octet unfulfilled. So each oxygen atom shares two pairs of electrons, forming a double bond, and both atoms achieve a complete octet.

This is why H₂ has a single bond while O₂ has a double bond.

Source: Chapter 4, Covalent Bonds / Versatile Nature of Carbon

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• The examiner expects you to clearly link number of valence electrons → electrons needed → bonds formed.
• Key terms to use: duplet (for hydrogen), octet (for oxygen), single bond, double bond, shared pair.
• Do NOT just state the result — briefly show the reasoning (how many electrons needed and why one/two pairs are shared). That's where the 3 marks lie: ~1 mark per element's reasoning + 1 mark for the conclusion/contrast.