The correct option is D 9
Let the digit to be filled is x.
∴x+5+3+1=x+9
For the number x531 to be divisible by 9,9+x should be multiple of 9.
x+9=9×n
For n=1,
9+x=9×1
⇒x=0
For n=2,
9+x=9×2
⇒x=9
However, for x=0,x531, i.e., 0531 is a three digit number.
∴ The possible digit that can fill in the blank is 9.