Question

Are the words christian, buddhist, hindu, and muslim proper nouns?

Answer 1

Yes
Christian, Buddhist, Hindu, Muslim

Explanation:

They are proper nouns because they are specific (referring to one believers of a religion by a name, rather than a general word such as religion which doesn't specify a religion). They must be capitalized.

Other examples of proper nouns:
Tokyo (names of cities)
Arkansas (names of states)
Zhejiang (names of provinces)
Canada (names of countries)
Oceania (names of regions)
Francis Crick (names of people)
Zoroastrianism (names of religions)

Answer 2

Yes

Explanation:

Proper nouns is to be specific.

Note: There is a difference between proper nouns and commons.

Ex: I am from the Middle East. << This is common. Because you are not being specific - there are a lot of countries in the Middle East.

Ex: I am from France. This is proper noun. Because you are being specific about what country you are from.

Christian, Buddhist, Hindu, and Muslim

I don't think I would consider Christian as a proper noun because there are different groups of Christianity.

For example, you have Catholic, Jehovah's Witnesses etc...they all considered as Christian.