is the number 1 a prime or composite number?
It's considered to be neither.
Composites can be written as the multiplication of at least two other factors, where the two factors are not that number.
For example, 2*3 = 6 means 6 is composite because you can write it out as a product of two other factors. You can't do that with the number 1, though. 1*1 = 1 is a true statement, but the two factors in the product are the same number as the number in question.
For prime numbers, you have to be able to point to two (and only two) divisors. But 1 has only a single divisor, the number 1.