English - Wheter and If

Whether and if can often be used interchangeably. However, there are some instances in which only one can be used.

ü  Both whether and if are used to introduce a yes/no question.

He asked me whether I felt well.

We’re not sure if they have studied.

ü  The verb “discuss” generally takes “whether” rather than “if”.

They discussed whether to invest in the new company.

ü  Use only whether after prepositions.

We talked about whether we should eat or not.

ü  Use only whether before infinitives.

She can’t decide whether to buy the bag or wait.

ü  Generally whether is considered more formal than if.

Source: Google