ref – https://www.grammarly.com/blog/is-vs-are/

The cat is eating all of his food.

The word ‘Cat’ is singular, so we use is

The cats are eating all of their food.

The word ‘Cats’ is plural, so we should use are.

The cat and the dog are eating as fast as they can.

We have more than one noun (the cat and the dog), we use ‘are’.

Collective Nouns

A collective noun refers to a group of people or things that is treated as a single entity in speech.

Committee is a collective noun – A committee is made up of multiple people, but the word itself is singular in form.

In American English, collective nouns take is.

example:

• The committee is considering the budget right now.
• The audience is getting antsy.
• The couple is moving to California.

Mass Nouns (Noncountable nouns)

Mass nouns (also called noncount nouns) are similar to collective nouns. They refer to things that can’t really be counted.

Sand and water are mass nouns. Mass nouns take is in both American and British English.
example:

• The sand is too hot to walk on!
• Water is our most precious resource.
• Pudding is very easy to make.

A number of (aka several) – use ‘are’

example:

A number of people are concerned about the lack of progress.

Group of (single entity) – use ‘is’

example:

That group of protesters is sure to be distracting.
This series of books is phenomenal.

There is vs There are

When choosing between there is and there are, you have to look at what comes after the phrase:.

There (is/are) a [cat] on the porch.

In the sentence above, cat is the subject, and since it is singular, it requires there is.

There (is/are) many [opportunities] to learn at this company.

In the sentence above, opportunities is the subject, and since it is plural, it requires there are. (Don’t let the word many throw you off—concentrate on the noun.)