Determine the number that logically replaces the question mark (?) in the following sequence.

12, 34, 53, 77, 94, 120, ?

The correct answer is 135.

To find the number that logically replaces the question mark (?) in the sequence, let us calculate the differences between consecutive terms:

$34-12=22$

$53-34=19$

$77-53=24$

$94-77=17$

$120-94=26$

The sequence of differences is: 22, 19, 24, 17, 26, ...

Now, let us examine the pattern in these differences by splitting them into two alternating sequences:

1. First alternating sequence (odd positions):

$22,24,26,\text{...}$

In this sequence, each number increases by 2 ($+2$).

2. Second alternating sequence (even positions):

$19,17,\text{...}$

In this sequence, each number decreases by 2 ($-2$).

The next difference needed to find the missing term is at an even position. Thus, we decrease the previous term (17) by 2:

$17-2=15$

Adding this difference of 15 to the last term of the given series (120) gives:

$120+15=135$