Hey there!

I'm not sure if you have learned the root test for analysis yet and so I will assume that you haven't

f) Notice that

This cannot possibly converge as the terms do not tend to zero as n tends to infinity. The root test would give an equal result

k) Note that, as n becomes large, . This is known to diverge by the integral test

l) Again, this sequence tends to the limit and so, as this is not zero, the series cannot converge

Hope that helps!