The number of shared pair of electrons in a molecule of methane is

Analyze the question The question asks how many pairs of electrons are shared (covalent bonds) in one molecule of methane, CH₄.

Explain the concept In a covalent bond, two atoms share a pair of electrons. Each single bond = 1 shared pair. So the number of shared pairs equals the number of single bonds in the molecule.

Step-by-step solution

1. Carbon (atomic number 6) has configuration 2, 4, so it has 4 valence electrons and needs 4 more to complete its octet.
2. Hydrogen (atomic number 1) has 1 valence electron and needs 1 more to complete its duplet.
3. Carbon shares one electron with each of 4 hydrogen atoms:

      H
      |
  H — C — H
      |
      H

4. Each C–H bond is one shared pair of electrons (one electron from C, one from H).
5. Number of C–H bonds = 4, so shared pairs = 4 (that is 8 shared electrons in total).

Watch out for the trap: Option D (8) is the number of shared electrons, not shared pairs. The question asks for pairs, so the answer is 4.

Answer: B (4)

Exam tip: For simple covalent molecules, count the bonds. CH₄ has 4 single bonds, so 4 shared pairs. Always check whether the question asks for "pairs" or "electrons," as WASSCE often tests this difference. (Similarly, NH₃ has 3 shared pairs and H₂O has 2.)