which of the following elements would have the greatest difference between the first and the second ionization energies mg al k ca sr

K

Explanation:

Ionization energy refers to the energy required to remove an electron from an atom. It usually increases across the period due to the increase in the size of the nuclear charge and decreases down the group due to increase in the number of shells.

If we look at the element, K, it has only one electron in its outermost shell. This implies that after this one electron is removed, the second ionization energy involves the removal of an electron from a filled shell.

This usually requires a lot of energy. Hence, the element having the highest difference in energy between first and second ionization energy is K.  

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c) should be the answer.