Countable and Uncountable Nouns

Countable nouns are the ones that can be counted and have a plural form, while uncountable nouns cannot be counted and do not have a plural form. However, there are certain nouns that can function as both countable and uncountable depending on the context.

- Countable nouns: These nouns refer to things that can be counted and have a plural form. For example, "tree" in the sentence "There are five trees in the park" is a countable noun because it can be counted and has a plural form ("trees").

- Uncountable nouns: These nouns refer to things that cannot be counted and do not have a plural form. For example, "air" in the sentence "Fresh air is good for your health" is an uncountable noun because it cannot be counted and does not have a plural form.

Explanation of the Correct Answer

The correct answer to the question is option B, "Air." "Air" can be both countable and uncountable depending on the context in which it is used.

- Countable usage: In certain contexts, "air" can be countable. For example, if we are referring to different kinds of air, such as "clean air," "polluted air," or "fresh air," we can use it as a countable noun. For instance, "There are three different airs in the room – cold, warm, and stale."

- Uncountable usage: In most cases, "air" is used as an uncountable noun. It refers to the invisible mixture of gases that surrounds the Earth. For example, "Breathing in fresh air is important for our well-being."

The context and the way the noun is used in a sentence determine whether it is countable or uncountable. In the case of "air," it is primarily used as an uncountable noun to refer to the general concept of the Earth's atmosphere. However, it can be used as a countable noun when we want to specify different types or qualities of air.

In conclusion, "air" is a noun that can be both countable and uncountable depending on the context in which it is used.

"Air" can be both countable (e.g., breaths of air) and uncountable (e.g., fresh air) depending on the context.