Find the missing group of letters in the following series. TS, ON, (), HG, FE

Which of the following letter-number clusters will replace the question mark (?) in the given series to make it logically complete? DAX 91, BVZ 83, ZQB 75, XLD 67, VGF 59, ?

Complete the given letter series: ABC, GHI, MNO, _______?

Which set of numbers will replace the question mark (?) to complete the following series logically? 13, 28, 49, 64, 85, ?