If CONTRIBUTE is written as ETBUIRNTOC, then which letter will be in the sixth place when counted from the left if POPULARISE is written in the same way?

Answer: Option D

Divide the word into five sets of two letters each and label these sets from 1 to 5. Then the code contains these sets in the order 5, 4, 3, 2, 1 with the letters of sets 5, 3, 1 written in a reverse order.
Thus, we have :
PO PU LA RI SE => ES RI AL PU OP
1 2 3 4 5 => 5 4 3 2 1