You shouldn't focus on the small details that are likely to be low yield for the MCAT. You should, however, focus on your approach to problems. In this case, there is a general way to approach such problems. How is strong vs. weak acidity defined? By the stability of the conjugate base. So all we need to do is assess the relative stabilities of F-, Cl-, Br-, and I-. Well, what factors are there to affect stability? Well, there's sterics (how big are they?) and electronics (how well is the charge stabilized?) - basically chemistry itself. So you have to weigh the relative sizes and the charge delocalization. If you can reason to this point for this problem, it should be enough. But you still need a little more specific knowledge that may be lower-yielding. That knowledge is that for the halogens, atomic radius is more important than electronegativity. In other words, while fluorine is very electronegative, the fact that it's so small makes the charge concentrated spatially and it doesn't like that. So fluoride is not particularly stable. Chloride is more stable and bromide even more stable. Therefore, HCl, HBr, and HI are strong acids whereas HF is a weak acid.
However, do not make the mistake of thinking that since HF is a weak acid, it's not as dangerous. In fact, it's more dangerous than HCl. This is because if HF gets on your skin, it's so small that it can easily permeate the skin. Once it gets through your skin and into your bloodstream, the fluoride that dissociates sucks the calcium out of your bones to form CaF2. This drives the equilibrium to the right so more HF dissociates and more Ca2+ is sucked out of your bones. People have been amputated and even died because they spilled HF on themselves.
