Can "who" substitute for " whom" in non-restrictive relative clause?

Question

1. Who/whom are you talking about?

2. Bill is a troublesome boy, whom(who?) you are talking about.

In the first sentence, who can substitute for whom. I wonder if who can do the same in the second sentence.

Answer 1

We can use the relative pronoun whom or who when it is the object of the verb.

Bill is the troublesome boy whom/who you are talking about.

In a restrictive relative clause we can leave out the relative pronoun when it is the object of the verb.

Bill is the troublesome boy whom/who you are talking about.➜ Bill is the troublesome boy you are talking about.

We use non-restrictive relative clauses to give extra information about the person or thing. It is not necessary information. We use commas in non-restrictive relative clauses.

In a non-restrictive relative clause, the relative pronoun cannot be left out.

Bill, whom/who you are talking about, is a troublesome boy.

We cannot use 'Bill, you are talking about, is a troublesome boy'.

(Edited)