Sipster 1.55:

c) Pumping length is 1. The smallest string in the language is length 0 and that is the empty string. The empty string cannot be pumped. The second smallest
   string in the language is length 1. That string can either be "1" or "0". Either string can be pumped, so the pumping length is 1.

f) Pumping length is 1. The only string in the language is the empty string. The pumping lemma requires there to be a string of at least length p to be
   pumped and the only string in the language is length 0, so p can be 1.

i) Pumping length is 5. The only string in the language is 1011. The pumping lemma requires there to be a string of at least length p to be pumped. 
   As there can't be a string of length 5 in the language, p can be 5. If the pumping length were 4 e

j) Pumping length of 1. The language is every string. So the pumping length can be anything since pumping a string will only yield another string. 
   Since the minimum possible pumping length is 1, the minimum pumping length of the language is 1.