Can l use whom instead of who in my example?

Question

Who the nominee will be has not been officially declared yet.

Note : as far as l know we can use "whom" providing that we us it in object position in noun clause .

Answer 1

In strict formal grammeer, if "whom" is correct, "who" is not. In current informal, and even much formal usage, "who" is used for both subject and object, and "whom" is never used. I suspect that in 100 years "whom" will be listed in dictionaries as obsolete. But it isn't obsolete at this time.

If you want a way to determine when "whom" is formally proper, see if "he" or "him" can be placed in roughly the same place in a modified statement. If "he" fits, use "who". If "him" fits "whom" is probably technically proper. Another way to tell: if the person is doing the action, use who; if the person is being acted on, "whom" might be proper. These should give the same result.

In the example sentence:

Who the nominee will be has not been officially declared yet.

"who" is proper" and "whom" would not be.

Consider that

He will be the nominee.

properly uses "he".

However, one could write:

We don't yet know to whom the nomination will be given.

When "whom" is used at all, it is often used directly following "to", as an object.

Answer 2

[Who the nominee will be] has not been officially declared yet.*

The simple answer is that when fronted "who" is a predicative complement, as it is here, it is always nominative; thus "who", not accusative "whom", is correct.