If I am not wrong, profit maximisation doesn’t always occur when MR=MC. MR=MC is just the first order condition and may signify a maxima or a minima. Dont you need to also check the second order condition?
So, the appropriate answer should be when the difference between revenue and cost (i.e. profit) is maximum
If this were a problem in a calculus class, then I’d agree that you need to check the convexity.
But this is a question in the economics section of a CFA exam. As a practical matter, you’re going to get a downward sloping marginal revenue curve and an upward sloping marginal cost curve. Where they cross you’ll have maximum profit, not minimum.
Also note that maxima and minima are plurals; you probably meant a maxim_ um _ or minim_ um _.