The answer is plural "like". A useful way to prove that a plural verb is correct in examples like yours is to front the preposition phrase:
1. "Of the boys (pl) who like (pl) playing football, Peter is one". (CORRECT)
2. "Of the boys (pl) who likes (sing) playing football, Peter is one". (WRONG)
In 1. plural "boys" matches plural "like", so "like" must be correct. But in 2. plural "boys" and singular "likes" is a mismatch, so "likes" must be wrong.
I have got it clearly now.
The verb 'is' agrees with the subject Peter (singular),
and the prepositional phrase 'of the boys' (plural)
forms the subject of the verb 'like'.
Which is third person plural.
I'm pleased with your great help, thanks.
I think Ralph is interested in the first sentence." Which form of the verb apply/applies here?"
In that sentence I took"which" to refer to both "likes and like" which would make the subject of that sentence. This is wrong because the "which" in my sentence complements the word "form" and together they make the subject of that sentence. "Form" here is singular and "applies" is the correct word to use.
So it is
Which form of the verb applies here?
Thanks
I'm so grateful.
I think Ralph is interested in the first sentence." Which form of the verb apply/applies here?"
In that sentence I took"which" to refer to both "likes and like" which would make the subject of that sentence. This is wrong because the "which" in my sentence complements the word "form" and together they make the subject of that sentence. "Form" here is singular and "applies" is the correct word to use.
So it is
Which form of the verb applies here?
Thanks
I'm so grateful.
You're making this unnecessarily complicated. You made a mistake in the wording of your question - simple as that. It should have been "Which form of the verb apply applies here"? The choice of which verb form to use has nothing to do with "which", which is merely a determiner, but to do with the head word of the subject which is "form". "Form" is clearly singular and hence the singular verb form "applies" is correct. (cf. the plural version, "Which forms of the verb apply here").