<p>Organic chemistry, Multivariable Calculus, Modern Physics</p>
<p>Many pre-med wanna-be’s hit a wall with Organic Chemistry, so I would say that’s the toughest course among the three. IMHO, the easiest would be Calc.</p>
<p>It depends on the thoroughness of your preparation in the prerequisite fields and your personal aptitudes / dedication.</p>
<p>For organic chemistry to be “easy”, you’d need a decent background in chemistry, be good at memorization, and find the subject interesting enough to spend serious time on. As gibby mentioned, it is very competitive.</p>
<p>If you’re good at math and have a solid understanding of singe variable calculus, multivariable wouldn’t be too hard, although if you’re considering a proof-based course for the first time it could be quite a shock. Can also be competitive.</p>
<p>Answering this question for modern physics is tricky because it depends on exactly what you mean by modern physics. If “modern” is Lagrangian rather than Newtonian mechanics, then it should be accessible before multivariable calculus (although it would be more standard to take multi, linear algebra, and diff. eq. before doing modern classical mechanics). If “modern” is basic mechanics with a little bit of special relativity, then it would probably be the easiest of the three. However, it seems most likely that “modern” means quantum, which would be very difficult without a grounding in calculus and especially linear algebra. I’d get some mechanics, E&M, and maybe thermodynamics / statistical mechanics under my belt before looking at quantum.</p>
<p>For me, MV would be easiest, then orgo, then Modern Physics.</p>
<p>I suspect that you’re referring to the summer versions of these courses, since “modern physics” is only taught during the summer (and so far for only one year; it may not return). Taking this into account (summer courses are often quite different from their term-time counterparts), my rankings would be, hardest to easiest,</p>
<p>Orgo
Multivariable
Physics</p>