@ goelmohit
i'll address this list, but i'll give you a warning / suggestion first.
CAVEAT:
this is one of those things that are RIDICULOUSLY hard to memorize, but is actually pretty easy just to
deduce from context. so, unless you're prepared to memorize a whole lot of easily confused, easily forgotten rules that are extremely subtle, you should just think about the context and go from there.
* for instance, given
X is only one of the factors, albeit an important one, that (keep/keeps) the market from spinning out of control
it's clear that there are MANY factors, ALL of which keep the market from doing blah blah blah, and that X is just one of them.
since there are MANY factors keeping...., we should use the plural "keep".
* on the other hand, given
X is the only one of the factors that (keep/keeps) the market from spinning out of control
it's clear that there are many factors, but NONE OF THEM EXCEPT X keeps the market from doing blah blah blah.
since X is the ONLY factor keeping...., we should use the singular "keeps".
in 99.9% of these, you'll be able to just think about the context in this way, saving yourself a horrendous amount of time and effort.
--
nevertheless, IF you still feel like killing yourself with memorization, then i'll indulge you.
1. One of the Xs that/who <plural>
if this is NOT preceded by "the" or "the ADJ", then this is always plural.
(context hint: if there's no "the" or "the ADJ", then there are many X's who do this)
2. One of the Xs <singular>
if this is "one of the Xs VERB"
and
NOT one of the Xs THAT verb",
then yes, this is always singular.
(context hint: nothing to indicate that any of the other Xs do this; only one is known to do it)
3. only One of the Xs <singular>
correct, as long as it's not "only one of the X's THAT..."
4. only One of the Xs that/who <singular>
this is 2 different cases.
if it's "
THE only one of the X's that/who...", then it should be SINGULAR.
if it's JUST "
only one of the X's that/who...", then it should be PLURAL.
--
let me emphasize again that memorizing these rules is about 65,535 times as hard as deducing the correct form from context.