Noun phrase or Not a noun phrase

1. If we think (the price of an item is too high), we won't purchase it, and the price will probably come down.

2. If you want to buy (a bottle of water while strolling) through Central Park, you may be in for a shock.

3. (The same brand of bottled water) you buy at home may cost twice as much in the New York City.

4. How much are you willing to pay for (a pair of athletic shoes), a new phone, or the latest video game?

A noun phrase is a group of words working as a single unit that is centered on a noun (also called the head of the phrase), and that may contain modifiers of that noun like numbers, determiners, quantifiers, or adjectives.

Based on this definition, we can answer whether the following phrases in parentheses are noun phrases or not.

1. If we think (the price of an item is too high), we won't purchase it, and the price will probably come down.

This is not a noun phrase because the construction is not centered on a noun only. Instead, it is a construction with a subject and a verb that expresses a thought, that is, it is a clause.

2. If you want to buy (a bottle of water while strolling) through Central Park, you may be in for a shock.

This is not a noun phrase either. The construction does not work as a single unit or a noun (We can prove that it is not a noun because it can not be replaced by a pronoun like "it" for example). Furthermore, "while strolling" is part of the phrase "through Central Park."

3. (The same brand of bottled water) you buy at home may cost twice as much in the New York City.

This is a noun phrase because it is centered on the noun "water" and contains determiners, adjectives, and prepositions that modify and further describe "water."

4. How much are you willing to pay for (a pair of athletic shoes), a new phone, or the latest video game?

This is also a noun phrase because it is centered on the noun "shoes," and the phrase also contains modifiers of that noun.