a) A series does not converge if the terms do not tend to zero. In this series the terms tend to 3/2.
b) A series converges if the absolute value of each term is less than the corresponding term of a series known to converge. In this case compare with the series 2/n^2.
c) A series converges if the ratio of successive terms tends to a limit k which is strictly less than 1. In this case the ratio of successive terms tends to zero.
d) Use one of the previous criteria: left as an exercise which one ...