The given numbers are 0,1,2,3
The ascending order of the given number is
0 < 1 < 2 < 3
Since we need a 4-digit number so it cannot start with 0. Hence we can place 0 in the second position.
Other than zero the smallest digit is 1 so we begin with 1.
Thus the smallest 4 – digit number formed is = 1038