For d). try multiplying the top and bottom by . I haven't done the maths myself yet, but that square root at the bottom is a pain! Try the same method with h.
For i), try diving both the top and bottom by .
For k, this seems like a sandwich rule question. I'm a little puzzled on it myself =S
For l, i'm not really sure. Since this is an alternating sequence and n is approaching infinity then the series can approach any limit in .