Final answer:
The correct answer is 'a. Validity,' since it refers to an instrument's accuracy in measuring what it's intended to measure, while reliability is about consistent results.
The right answer to the student's question is therefore a. Validity.
Step-by-step explanation:
If a calculator subtracts numbers when you push the addition button, you would question the validity of the addition button because it doesn't do what it is supposed to do. Validity refers to the extent to which a given instrument or tool accurately measures what it's intended to measure.
Validity refers to the extent to which a given instrument or tool accurately measures what it's supposed to measure. In this case, the addition button on the calculator is not functioning correctly and subtracts numbers instead of adding them, so it does not accurately measure addition. Therefore, you would question the validity of the addition button.
On the other hand, reliability refers to the ability to consistently produce a given result. In the case of the calculator, the addition button is not providing a valid result, even if it is consistently subtracting (which would be reliable but incorrect). The right answer to the student's question is therefore a. Validity.