Answer:
The square root of a prime number is always an irrational number, then the product of the square root of a prime number and a nonzero rational number is equivalent to:
"the product of an irrational number and a rational number different than zero...."
We know that the product of an irrational number and a rational number (different than zero) is ALWAYS an irrational number.
Then "When is the product of the square root of a prime number and a nonzero rational number a rational number?"
Never, the product will always be irrational.