The missing term of the series is A2, C5, E8, G11, ____

Break the series in 2 parts (Alphabetical and numerical):

A, C, E, G, ? and 2, 5, 8, 11,?

Now, lets find the next term:

A(1) ⇒ +2 ⇒ C(3) ⇒ +2 ⇒ E(5) ⇒ +2 ⇒ G(7) ⇒ +2 ⇒ I(9)

and

2 ⇒ +3 ⇒ 5 ⇒ +3 ⇒ 8 ⇒ +3 ⇒ 11 ⇒ +3 ⇒ 14

Hence, I(14) will be the next term.