Select the option that is related to the fifth letter-cluster in the same way as the second letter-cluster is related to the first letter-cluster and the fourth letter-cluster is related to the third letter-cluster.
TIDE:URBW::BACK:CZAQ::WORD:?

Let's look at the pattern between the first and second letter-clusters:
TIDE→URBW

T+1=U

I+9=R (or opposite letter I↔R)

D−2=B

E↔V, then +1=W (or opposite pair relation)
Let's look at numerical differences:

T(20)→U(21)⟹+1

I(9)→R(18)⟹+9 (or opposite letter)

D(4)→B(2)⟹−2

E(5)→W(23)⟹−8 or +18

Let's test with BACK→CZAQ:

B(2)→C(3)⟹+1

A(1)→Z(26)⟹−1 (or opposite letter)

C(3)→A(1)⟹−2

K(11)→Q(17)⟹+6

Let's reconsider the opposite letters logic:

1st letter: +1

2nd letter: Pairs of opposites (I↔R, A↔Z). For WORD, the opposite of O is L.

3rd letter: −2 (D−2=B, C−2=A). For WORD, R(18)−2=P(16).

4th letter: Let's check the relationship for the last letter:

In TIDE→URBW: E's opposite letter is V(22), then +1=W(23).

In BACK→CZAQ: K's opposite letter is P(16), then +1=Q(17).

For WORD: D's opposite letter is W(23), then +1=X(24).

Applying this established pattern to WORD:

W+1=X

Opposite of O=L

R−2=P

Opposite of D=W
+1

​
X

Hence, the resulting cluster is XLPX.