Which of the following is NOT a statistical hypothesis?

A statistical hypothesis is a statement about a population parameter. b, c and d are referring to population parameters (and yes, vadge, p is a population proportion, so it is fine). Now you didn't say whether a) is about a population variance or a sample variance. If it is about a population variance, then all of them are statistical hypotheses. If it is a sample variance, then a) is not a statistical hypothesis.