A rational expression is undefined whenever its numerator is zero.

False

Step-by-step explanation:

for a rational number expressed as (A / B) where A & B are integers

if the numerator (A) is zero, then (A/B) is simplify zero

i. e (A / B) = (0 / B) = 0

however if the denominator (B) is zero, then by definition any value divided by zero is undefined.

(A / B) = (A / 0) = {undefined}