etc_host

Gee, not really. It's still multiple choice.

I simply left out the incorrect responses B, C, D and E, in my version.

Here, let me show you:

  Q. What does idempotence mean?

  A. Validating a sequence of events in a stateless fashion.

  B. A river in Egypt.

  C. Many things to many people.

  D. Anything you want.

  E. I don't know.

There. It's multiple choice now. See how that works?

The question "why is this useful?" is akin to "why do we like a thing?" and liking a thing is an opinion, and the reason for liking something carries a motivation, which differs from simply knowing what a thing is.

Why is it objectively useful? Well, it's not. Idempotency is neutral. It can be as useless as it is useful. Knowing what it is matters more than a cargo cult desire to find utility in a vocabulary quiz.

Should a test verify that an individual's opinion aligns with a trend expressing a point of view, or should it verify awareness of concepts?

Just request the meaning of the word itself. Don't load the question with trendy concepts.

  Q. What does idempotence mean?

  A. Validating a sequences of events in a stateless fashion.

As an addendum, a follow-up question might add concrete context to the idea being tested. But context is a bottomless pit, where the default answer "it depends" lurks. That makes this a bad question.

You are incorrect in stating that this is not an opinion-based question, since the dictionary definition of the word itself is not the correct answer.

  Question 2 of 20

  Which of the following is a valid reason for why idempotence is useful in API design?

  A. Due to the rise of distributed systems, idempotence has become necessary in order to scale any large-scale application.
  B. Given the unreliability of networks, idempotence allows developers to build robust API’s that allow for retry attempts.
  C. Idempotence is actually not as useful in API design and is instead more useful when designing database schemas.
  D. Idempotence is important to prevent clients from sending multiple duplicate API requests.
  E. I don't know

Wow, you're really going to try and estimate my level, based on opinions? No thanks. Not without a write-in option.

P.S. My opinion is that, idempotence only useful, if you draw the conclusion that ceding control of your systems to external entities is useful. At which point you compromise your system based on communicated assumptions for how something should be, and not necessarily how things are behind the wall you can never see the other side of. In other words, the subtext of this question is:

  Do you like delegation of responsibility? The correct answer is yes.

Meanwhile, this question deals in buzz-wordy jargon. The answer you may provide, cannot be presumed as correct, without proper interpretation of the dictionary definition, according to the popularity of in-group consensus, and the chaining of the awareness of other preferred buzzwords as social cues for the expectation of a proper answer.