The first two letters, PQ, are static.
P5QR,
P4QS,
P3QT, _____,
P1QV
The third letter is in alphabetical order,
P
5Q
R, P
4Q
S, P
3Q
T, _____, P
1Q
V beginning with R.
P
5Q
R, P
4QS, P
3QT, _____, P
1QV
The number series is in descending order beginning with 5.
P
5QR, P
4QS, P
3QT, _____, P
1QV
so, the correct and is:
P2QU