In the following cases, decide whether the set M is $$limited up or down.

Discuss the existence of a minimum, maximum, infimum and supremum of the set M in Q$.$

M :$=\{x$ in $Q|2<x^2<4\}$;

M :$=\{x$ in $Q|x=\frac{2}{3+n}$ for $nin{N}_0$