It is 1.
0
A single number cannot produce a product.
Assuming the question is about positive integers and there are no leading 0s, the answer is NEVER.
-9999. Or, if only positive numbers are being considered, then, 1000.
The largest single digit composite number is 9. The largest prime number is 17 million digits long. The definition of a composite number is any number that has at least one positive divisor other than one or the number itself (it is not a prime number). The largest composite digit is therefore longer than the largest prime number by at leaf +1.
The number 10 has a roman numeral of X. The number 50 has a roman numeral of L. These are the only 2 digit numbers with a single value.
The least possible integer is -98765432. The least possible positive integer is 10234567.
A 6-digit number will ALWAYS be greater than a 5-digit number. Assuming both are positive of course.
Since the 1-digit number is explicitly required to be positive but the 2-digit number is not so constrained, the obvious solution is to make the 2-digit number negative. This gives 9*(-99) = -891
7
4 is the least one digit composite number