What is the chemical symbol of magnesium?

The correct answer is option 4. Mg.

The chemical symbol of an element is a one or two-letter abbreviation used to represent that element. In the case of magnesium, its chemical symbol is "Mg." Each element has a unique chemical symbol, which is derived from either the English name or the Latin name of the element.

Here's a brief explanation of each option:

1. Mn: This is the chemical symbol for manganese, not magnesium.

2. Ms: This is not a valid chemical symbol for any known element.

3. Ma: This is not a valid chemical symbol for any known element.

4. Mg: This is the correct chemical symbol for magnesium. Magnesium is a chemical element with the atomic number 12 and is represented by the symbol Mg in the periodic table.

So, the correct answer is option 4. Mg.