A noun is a person, place, thing/animal, or idea. A proper noun is one of those things but very particular (it is highly likely that there is only one of it, with the exception of people's names/titles). A proper noun is written with the first letter capitalized.
1. "clouds" is the noun, as it is an object. It is improper because it is not capitalized and not a specific thing (there are many clouds).
2. "Utah" is the noun, as it is a place. It is proper because it is capitalized and is particular (there is only one Utah).
3. "The White House" is the noun, as it is a place. It is proper because it is particular.
4. "(Uncle) Henry" is the noun, as it is a person. It is proper because it is a person's name.
5. "Apartment" is the noun, as it is a thing/place. It is improper because it is not particular.
(All of the sentences have pronouns, e.g. I, they, we, etc., but that is not what the worksheet is looking for.)