Why is it easy for a magnesIum(mg number 12)

To lose 2 electrons.

Is it because the nuclear charge of the mg atom is relatively weak?

Yes, the ease with which an atom can lose electrons depends on the nuclear charge or the positive charge of the nucleus. In the case of magnesium (Mg), it has an atomic number of 12, meaning it has 12 protons in the nucleus.

The nuclear charge of magnesium is not particularly weak, but it is not as strong as elements with higher atomic numbers. This is because the nuclear charge of an atom is determined by the number of protons in the nucleus.

However, the key factor that makes it relatively easy for magnesium to lose 2 electrons is the electron configuration of the atom. Magnesium has a total of 12 electrons, with two in the first energy level and eight in the second energy level. The outermost energy level, known as the valence shell, contains only two electrons.

To achieve a stable electron configuration, atoms tend to gain, lose, or share electrons. In the case of magnesium, losing 2 electrons from its valence shell would result in achieving a stable electron configuration similar to that of a noble gas, neon (which has 10 electrons in total).

Since the valence electrons are relatively far from the nucleus and experience a weaker attractive force, it is easier for magnesium to lose its two valence electrons compared to elements with higher nuclear charges and more tightly held electrons.