“Do you know if it's mandatory?”

There's a meeting scheduled for this afternoon. You're busy with other work and don't really want to go. You're not sure whether attendance is required at this meeting. When a coworker asks if you're going, you ask this.

Do you know if it's mandatory?

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Do you know if (clause)?

In casual spoken English, people often ask, "Do you know if ___?" to find out the answer to a "Yes" or "No" question. For example:

Do you know if you're having a boy or girl?

Do you know if he's awake?

Answers to "Do you know if...?" can include:

Yes, it is.

Yeah, he is.

No, they're not.

No, I don't think so.

I'm not sure.

No, I don't know.

In formal English for writing and for situations where you don't know people well, you usually use "whether" instead of "if":

Do they know whether the child is a boy or a girl?

(something) is mandatory

When you say that something "is mandatory", it means that you have to do it. Examples of things that are "mandatory" include:

  • a mandatory meeting
  • mandatory reading (books you have to read for a class)
  • mandatory retirement (making people retire when they reach a certain age)
  • mandatory military service (men in some countries have to serve in the military for a few years)