**The oxidation number of an element tells us about the charge on the central metal atom.**

The oxidation number of an element is a number that represents the charge that an atom would have if electrons were transferred completely. It is a measure of the degree of oxidation of an atom in a compound. The oxidation number can be positive, negative, or zero, depending on whether the atom loses, gains, or shares electrons.

**Explanation:**

**1. Definition of oxidation number:**
The oxidation number is a concept used in chemistry to track the distribution of electrons in chemical compounds. It is a number assigned to each atom in a molecule or ion to indicate its degree of oxidation or reduction. The oxidation number can be positive, negative, or zero.

**2. Charge on the central metal atom:**
The oxidation number of an element tells us about the charge on the central metal atom in a compound. For example, in the compound sodium chloride (NaCl), the oxidation number of sodium is +1 because it loses one electron to form a positive ion, while the oxidation number of chlorine is -1 because it gains one electron to form a negative ion.

**3. Number of electrons gained, lost or shared:**
While the oxidation number does not directly tell us about the number of electrons gained, lost, or shared by an atom, it provides information about the redistribution of electrons in a compound. By assigning oxidation numbers to the atoms in a compound, we can determine how electrons are transferred or shared between atoms during a chemical reaction.

**4. Degree of oxidation:**
The oxidation number also gives us information about the degree of oxidation of an atom in a compound. The term "oxidation" refers to the loss of electrons, and the oxidation number indicates the extent to which an atom has lost or gained electrons. A higher positive oxidation number indicates a greater degree of oxidation, while a negative oxidation number indicates a reduction.

**Conclusion:**
In summary, the oxidation number of an element tells us about the charge on the central metal atom in a compound. It provides information about the redistribution of electrons in a compound and indicates the degree of oxidation of an atom. Therefore, the correct answer is option 'A' - the oxidation number of an element tells us about the charge on the central metal atom.