Sentence Correction

I heard once in one GMAT training institution (let's call it A)that a singular pronoun can not be used to refer a plural antecedent.
For instance, the melting points of most metallic elements are hundreds of degrees above the room temperature, but that of mercury is below the freezing point of water.

Here, in the second clause, the author omitted the phrase 'the melting point' and put 'that' instead.
This way is wrong because the author use a singular pronoun 'that' to refer the antecedent, which, in this case, is the melting points.
BUT I saw this sentence in another institution(institution B)'s tutoring video. and It's a correct expression, according to this video.
I'm confused in this paradox, please tell me which one is nearer to the truth.

Ali Tariq wrote:All what A says about that is correct!
B is incorrect here.

the melting points of most metallic elements are hundreds of degrees above the room temperature, but that of mercury is below the freezing point of water.

that cannot refer to melting points.
those, on the other hand, would also have been incorrect.

thank you for your verification.
Because we can't change the plural form " the melting points" into " the melting point" in the first clause,(that would suggest that all metallic elements share the same melting point, violating the common sense),the correct answer will be: the melting points of most metallic elements are hundreds of degrees above the room temperature, but the melting point of mercury is below the freezing point of water. ( rewrite the phrase)? correct me if I'm wrong.

Ali Tariq wrote:

thank you for your verification.

Pleasure!

Because we can't change the plural form " the melting points" into " the melting point" in the first clause,

Correct!

(that would suggest that all metallic elements share the same melting point, violating the common sense)

Correct!.
The logical error in this case will be noun-noun disagreement(if you want to be a little more specific).

the correct answer will be:
the melting points of most metallic elements are hundreds of degrees above the room temperature, but the melting point of mercury is below the freezing point of water.
( rewrite the phrase)?

no pronoun error,
no logical (noun-noun disagreement) error,

correct me if I'm wrong

You are right.

HI, ALI,

LOL!
I dusted off my English after three years of graduation from college and began to prepare the GMAT 20 days ago, then I realized that there's a long way to go.
thank you again for your quick reply! this really encouraged me.

I think the sentence has a different mistake then the one you said. You did correct the sentence but there is a smaller error and you changed more than needed.

o The melting point of most metallic elements is hundreds of degrees above room temperature, but that of mercury is below the freezing point of water (demonstrative pronoun is that which refers to melting point, that is singular cuz referring to one melting points, that not 100% identical to the antecedent but similar category)

It should be is not are as melting point is the subject and of most metallic elements is the modifier. That refers to the antecedent melting point so that is correct. Unfortunately, I had been using this prep to help myself study for a long time and no wonder I made so many errors. It sucks when the prep courses teach errors. I only noticed it now as I reviewed and searched google and this came up. So thanks for posting it.

I was about to remove it from my study materials as wrong but this confirms it.