Final answer:
The expression 2/x is undefined when the denominator x is equal to zero, as division by zero is undefined.
Step-by-step explanation:
The expression given is 2/x. For this expression to be undefined, the denominator must be equal to zero because division by zero is undefined in mathematics. This means that the value of x that makes the expression undefined is x = 0. It's important to note that any real number divided by zero does not result in a real number, which is why the expression is considered undefined at x = 0.