Whether or If? Can’t decide which one to choose? Here is a simple rule.

When you want to introduce a condition use If. If you continue to be rude, I shall leave the room. The condition is clear here.
When you talk of two alternatives, use Whether. Whether the minister comes or not, the meeting will take place. Whether is followed by “or not” to show alternative choices, but sometimes it is implied. He doesn’t know whether he is free to speak. [or not.]
Choices can be of different kinds. You need to decide whether you will go to the party of stay home and study. I don’t know whether to laugh or cry.

That said, you will find that the two words are sometimes inter-changeable. Mother doesn’t know whether her aunt is coming or not. Mother doesn’t know if her aunt is coming.
In either sentence, the meaning is that the aunt may or may not come.

Watch our for the sentences where you cannot inter-change Whether and If.

Mother doesn’t know whether her aunt is coming on Monday or Tuesday. Here, the two possibilities are mother’s aunt could come on Monday or she could come on Tuesday. Now, read this:
Mother doesn’t know if her aunt is coming on Monday or Tuesday.
In this sentence the two possibilities are: the aunt could come on Monday or she could come on Tuesday.
There is a second possibility. “If her aunt is coming” tells you the aunt may not come at all! To avoid this confusion, use whether where you have two choices and use if where there is a clear condition.

Read these and you ‘ll get it.
Tell me if you plan to visit Kashmir this summer. [Tell me only if you decide to go to Kashmir.]
Tell me whether or not you plan to visit Kashmir this summer. [Tell me anyway.]

Back to square one: Use If for a condition, use Whether for two choices. You cannot go wrong.

Quiz: Choose Whether or If, appropriately.
[1] ______we save carefully, we will be able to visit Europe next summer.
[2] I honestly can’t tell you __________ this plan will work.
[3] ______you can’t say something nice, don’t say anything at all.
[4] She has to decide ___________ she will study radiology or robotics.
[5] I don’t know __________ I should continue to trust him.
[6] The town didn’t know ______ that was good news.
[7] You need to decide __________ you can keep quiet about the matter.
[8] She says she doesn’t know __________ to laugh or cry.