Singular or plural verb?

I was reading a textbook and this sentence came up:

Water is one of the few substances that are less dense as a solid than as a liquid.

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Why is it the verb "to be" plural, and not singular? I would say:

Water is one of the few substances that is less dense as a solid than as a liquid.

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It's as though are refers to substances, but to me it seems to make more sense that it should refer to water, which is uncountable. Water goes with is, not are, right?

Could someone clear this up? Thanks.

I agree with you. Let's see if there are other opinions.

My opinion is based on the fact that the sentence could be reduced as below:

Water is [one of the few substances that are] less dense as a solid than as a liquid.

The relative pronoun 'that' refers back to 'substances' (plural)' There are a few substances that are less dense as a solid than as a liquid. Water is one of these.

Chicken Sandwich said:

Why is it the verb "to be" plural, and not singular?

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***** NOT A TEACHER *****


Tom: Water is one.

Mona: One of what?

Tom: The few substances that are less dense as ....

*****
People say that The Times of London used to be one of the newspapers that

were carefully read by world leaders.

P.S. Of the few substanceS that ARE less dense as a solid than as a liquid, water

can be counted as ONE of THEM.

No the correct verb is "are"

There are a few substances that are less dense as a solid than as a liquid. Water is one of these. Therefore, water is one of [those substances (pl) that are less dense as a solid than as a liquid.] You've already used the correct verb (is) for water; now you need to use the correct verb (are) for substances.

What is water one of? It one of those plural, multiple, substances that are less dense as a solid.

Is there a serious grammarian who would dispute this?

Of the few substances that are less dense as a solid than as a liquid, water is one.

Re: Singular or plural verb? (not a teacher)

Water is one of the few substances that are less dense as a solid than as a liquid.
Let us first clarify what message do you really want to convey. If you just want to emphasize the difference in density of water in two different states, simply say, Water is less dense as a solid than as a liquid." However, if you wish to downplay the emphasis on the unique feature of water and instead qualify it as just one of the few substances, then you are shifting the thought to the word substances which now requires plural form of "to be." :-o