Given: x is rational number and y is irrational number.

Yes, xy is necessarily an irrational number.

Example: Let x = 2, which is rational.

Let y = √2, which is irrational.

Then, x × y = 2 × √2 = 2√2, which is again irrational.

Also, consider the case when x = 0.

Then xy = 0, which is rational.

∴ Product of a rational and an irrational number is always irrational, only if the rational number is not zero.