Answer:
Its outer electron is in the 3p-orbital which is slightly further from the nucleus and is shielded by the 3s-orbital and is therefore requires less energy to remove than the magnesium's outer electron which is closer and not as shielded.
Explanation:
Think of it as going to grab something. Are you going to want to grab the closest item or walk another 30 feet to get something else? Most would choose the shorter path and that is what these electrons do also.
