The trend for ionization energy is a general increase from left to right across a period. However, magnesium (Mg) is found to have a higher first ionization energy value than aluminum (Al). Explain this exception to the general trend in terms of electron arrangements and attraction/repulsion.

So in your question that ask to explain the exception to the general trend in terms of electron arrangements and attraction/repulsion the answer would be the following:

Margnesium = 1s2 2s2 2p6 3s2 has a higher ionization energy

Aluminum is = 1s2 2s2 2p6 3s2 3p1 has a one unpaired electron 3p1 that could easily be removed.