Using ---- Whether and If
1). After Prepositions , we use only whether.
I haven't settled the question of whether I'll go back home.
There was a big argument about whether we should move to a new house.
2). Whether, but not if, is used before infinitives.
They can't decide whether to get married now or wait.
3). When a question-word clause is a subject or complement, whether is preferred.
Whether we can stay with my mother is another matter. - (Subject)
The question is whether the man can be trusted. - (Complement)
The question is if the man can be trusted. - Correct but less preferred.
4). If an indirect question is fronted , whether is used.
Whether I'll have time I'm not sure at the moment.
5). Whether is generally preferred in a two - part question with or.
The Directors have not decided whether they will recommend a dividend or reinvest the profits.
6). After verbs that are more common in a formal style, whether is preferred.
We discussed whether we should close the shop.
7). Whether and if both can introduce indirect questions.
I'm not sure whether / if I'll have time.
8). Yes / No questions are reported with if or whether.
I don't know if / whether I can help you.
The link below further clarifies the use of "whether" and "if"
whether vs if
Note - The word IF does not always signal a conditional sentence. In such cases, the GMAT prefers "whether" instead of "if"
I don't know if I will go to the dance. (Incorrect)
I don't know whether I will go to the dance. (Correct)
Click on link below and view sentence no. 45 and 46 for the above rule.