is the smallest five-digit number that can be formed using 4, 3, 1, 7, and 9 without repeating any digit.

The correct option is C 13,479
Arrange the digits in the increasing order of their values.
1 < 3 < 4 < 7 < 9
Place the smallest digit at the largest place and arrange the remaining digits in an increasing order.
Thus, the smallest five-digit number that can be formed is 13,479.