If p and q are two prime number,

It is given that p and q are two prime numbers; we have to find their HCF.

We know that the factors of any prime number are 1 and the prime number itself.

For example, let $p=2$ and $q=3$

Thus, the factors are as follows

$p=2 \times 1$

And

$q=3 \times 1$

Now, the HCF of 2 and 3 is 1.

Thus the HCF of p and q is 1