1. 

In the following question find out the group of the letters in the place of question in the letter series.

1/R, 3/O, 5/K, 9/F, 13/Z, ?

A. 19/S
B. 20/T
C. 19/T
D. 21/R

Answer: Option A

Explanation:

Pattern of the series as shown below

letter-and-symbol-series-logical-reasoning-practice-level---letter-and symbol-series-problems

Hence, the missing term is 19S.