The answer is C, the best way to tackle these sort of questions is write out what each atom is, find it’s place on the periodic table and look for the trend. Ionisation energy tends to relate to atomic radii, the smaller the radii the higher the IE, you can look into something called effective nuclear charge which talks about shielding and something called penetration. But back to the question, the answer is C because as you know as you go along the period, the nuclear radii drops which means a higher overall IE, of course you have some exceptions to this such as aluminium and sulphur, but don’t worry about these kinda questions too much, I’m assuming it’s a 1 marker? (Haven’t done a level chemistry in over 5 years).