Find the number that can replace question mark (?) in the series given below:

9, 3, 11, 1, 13, -1?

The correct option is 15.

To find the missing number in the series, let us analyze the pattern of the given sequence:
9, 3, 11, 1, 13, -1, ?

This sequence is an alternating series, which is composed of two separate mathematical progressions interwoven together.

1. The first alternating series (occupying the odd positions: 1st, 3rd, 5th, and 7th terms):
The sequence of numbers is: 9, 11, 13, ?
Let's find the difference between consecutive terms in this sub-series:

$9+2=11$

$11+2=13$

We can see that the pattern is to add 2 to each consecutive term. Applying this same pattern to find the next term (the 7th term in the main series):

$13+2=15$

2. The second alternating series (occupying the even positions: 2nd, 4th, and 6th terms):
The sequence of numbers is: 3, 1, -1
Let's observe the progression rule for this sub-series:

$3-2=1$

$1-2=-1$

Here, the pattern is to subtract 2 from each consecutive term.

Since the question mark (?) is at the 7th position (an odd position), it belongs to the first alternating series. Therefore, the number that replaces the question mark is 15.