Which of the following letter-number clusters will replace the question mark (?) in the given series to make it logically complete?
JNR -1, LPO -2, NRL -4, ?, RVF -16

JNR -1, LPO -2, NRL -4, ?, RVF -16

Numbers: 1, 2, 4, ?, 16

This is clearly doubling each time:

1 × 2 = 2

2 × 2 = 4

4 × 2 = 8

8 × 2 = 16

So the missing number is 8

First Letters:
J (10) + 2 = L (12)
L (12) + 2 = N (14)
N (14) + 2 = P (16)
P (16) + 2 = R (18)
First letter: P
Second Letters:
N (14) + 2 = P (16)
P (16) + 2 = R (18)
R (18) + 2 = T (20)
T (20) + 2 = V (22)
Second letter: T
Third Letters:
R (18) - 3 = O (15)
O (15) - 3 = L (12)
L (12) - 3 = I (9)
I (9) - 3 = F (6)
Third letter: I​​