The correct option is A 9C3
Let the six digit number be x1x2x3x4x5x6
Such that
x1<x2<x3<x4<x5<x6
Clearly no digit can be zero. Also, all the digits should be distinct.
So, let us first select six digits from the list of digits
1,2,3,4,5,6,7,8,9 which can be done in 9C6 ways.
After selecting these digits they can be put only in one order.
Thus, the number of such numbers
= 9C6×1=9C3