Is this sentence correct?

Mrs. Jones is one of those doctors who ARE always prompt with THEIR dictation.

(i read that one in an online module. i thought "one of the or those [plural noun] takes a singular verb. i got confused. what is the rule regarding the use of "one of those" and "among those" )

thank u

[Casiopea]

"who" is neither singular or plural. It gets its number agreement from its referent. Now, in our example sentence, that referent is "one of those doctors", a phrase made of up two nouns, singular "one" and plural "those doctors. And given that variety, speakers will interpret the referent in one of two ways:

(1) "who" refers back to "one", the head of the phrase, and thereby agrees in number with singular "one":

Mrs Jones is one of those doctors who is ...

(2) "who" refers back to the closest noun, "those doctors", and thereby agrees in number with a plural noun:

Mrs Jones is one of those doctors who are ...

From a pure grammatical standpoint, (1) meets the requirements, whereas (2) is an extension of the rule. That rule being, the verb agrees in number with the head noun, not its object:

Agreement Rule
Head noun: one
Object: those doctors
Verb: is

Extension
Head noun: one
Object: those doctors
Verb: are

In short, both (1) and (2) are acceptable. Structure is meaning, though, so they do mean different things:

(1) one of those who is <an individual associated with a particular group>
(2) one of those who are <the group as a whole>

Welcome, Anon.