**(D) 22**

**From the question it is given that, the ratio of red marbles to blue marbles is 7:4.**

Now, let us assume the common factor of 7 and 4 be x.

So, the total number of marbles in the box = 7x + 4x = 11x

Hence number of marbles in the box is a multiple of 11.

**Therefore, 11 × 2 = 22**