Find the missing number?

Answer: Option B

Logic:

Sum of the Four Number at the corner of the square = 21 and
Sum of the Four Number at the middle of the square = 21.

Now,
7 + 5 + 6 + 3 = 21
5 + 7 + x + 8 = 21
x = 1.
Thus,
Missing Number = 1.