Salut Lihini,

After negation the indefinite article "un" becomes de, but d' before a vowel.

So I agree that your proposal is correct.

You have not included the Kwiziq lesson or question from where this query comes.

Bonne journée

Jim

No, this is wrong. The correct sentence is given as one of the examples in the Kwiziq lesson below:

Un/une become de/d' in negative sentences in French (French Indefinite Articles)

Non, il ne reste pas un ami loyal !

The explanation is also given in the lesson:

This rule does NOT apply to sentences using the verb être and other List of French "state verbs" - "verbes d'état", with which the indefinite article doesn't change.

Perhaps it's important to point out that the translation is: "No, he doesn't remain a loyal friend!"

I suppose it could also have been something like: "No, there aren't any loyal friends remaining", when "pas d'ami" might be correct. "Pas de" always has the sense of "not any".