Here is the correct matching of each element to the number of electrons in its valence shell:
- Carbon (C) - A) Four
- Hydrogen (H) - B) Two
- Magnesium (Mg) - C) One
- Oxygen (O) - D) Six
So the matches are:
- Carbon (C) - A
- Hydrogen (H) - B
- Magnesium (Mg) - C
- Oxygen (O) - D