Select the option that is related to the third term in the same way as the second term is related to the first term.
OBSTACLE:BOXOFXEL::COLLOSAL:?

Let's carefully analyze the letter transformation rule from OBSTACLE to BOXOFXEL:
Let's divide the 8-letter word into two halves:

First half: O B S T

Second half: A C L E

Let's observe how O B S T transforms into B O X O:

Look at the first two letters swapped: O B→B O

Look at the next two letters: S(19)+5=24(X), T(20)−5=15(O)

Let's see if this matches the second half A C L E transforming into F X E L:

Look at A C: A(1)+5=6(F), C(3)−5=−2=24(X)

Look at L E swapped: L E→E L

Let's organize this structure cleanly:

Letters 1 and 2: Swapped →O B→B O

Letters 3 and 4: +5,−5→S+5=X,T−5=O

Letters 5 and 6: +5,−5→A+5=F,C−5=X

Letters 7 and 8: Swapped →L E→E L

Let's perform this exact set of structural mutations on COLLOSAL:

1 and 2 (C O): Swapped →O C

3 and 4 (L L):

L(12)+5=17→Q

L(12)−5=7→G

5 and 6 (O S):

O(15)+5=20→T

S(19)−5=14→N

7 and 8 (A L): Swapped →L A

Combining these blocks gives: O C Q G T N L A.