Data-Sufficiency:
Question: Who among P, Q, R, S and T is the lightest?
(I) R is heavier than Q and T but lighter than S.
(II) S is not the heaviest.
From I, we have: R>Q, R>T, S>R i.e. S>R>Q>T or S>R>T>Q.
From II, S is not the heaviest. So, P is the heaviest.
Thus, we have: P > S > R > Q > T or P > S > R > T > Q.
Hence, either T or Q is the lightest.