Select the number that can replace the question mark (?) in the following series.
2, 7, 5, 2, 3, 1, ?

The logic for the given series is that a number is equal to the positive difference of previous two numbers as shown below

$$\left|7-2\right|=\left|5\right|=5$$

$$\left|5-7\right|=\left|-2\right|=2$$

$$\left|2-5\right|=\left|-3\right|=3$$

$$\left|3-2\right|=\left|1\right|=1$$

Similarly, the next number is

$$\left|1-3\right|=\left|-2\right|=2$$

$$\therefore\ $$The required number is 2

Hence, the correct answer is Option A