To form the smallest number, arrange the digits in ascending order. However, a number cannot start with zero if it is to be a 6-digit number. So, place the smallest non-zero digit first (1), followed by 0, and then the remaining digits in ascending order (2, 3, 5, 7). This results in 102357. Option B is incorrect because 012357 is essentially a 5-digit number. Options C and D have incorrect ordering of digits.