There are total 9 compound propositions, out of which 6 contain ∼s. So if we assign s as false, these 6 propositions will be true. In remaining 3 compound propositions, two contain p and the third contains ∼r. So if we assign p and r as true and false respectively, these 3 propositions will also be true. Hence maximum number of propositions that can be true are 9.