Your answer is the first option, "One is a factor of every whole number since every number is divisible by itself".
This is true because whenever you multiply 1 by anything you always get the thing you multiplied by, which makes it a factor of every number.
You can also find this by eliminating the other options, for example a prime number is any number whose factors are 1 and itself, 2 factors, so since 1 only has 1 factor it is not prime and option 3 is eliminated.
This also eliminates option 4 because 1 cannot be a composite number if it only has 1 factor.
I hope this helps!
