Yes, the word "Venus" is capitalized because it is the name of a planet.
The word "chemistry" should be capitalized only when it is at the beginning of a sentence or part of a title.
Nouns are not are not always capitalized. A common noun is a word for any person, place, or thing. A common noun is capitalized only when it is the first word in a sentence. A proper noun is the name of a specific person, place, thing, or a title. A proper noun is always capitalized.
When it is at the start of a sentence.
No, the word "equator" should not be capitalized unless it appears at the beginning of a sentence or as part of a proper noun (e.g., Equator Line Cafe).
No, but it is just one word: saltpeter.
No, it shouldn't be capitalized.
No it shouldn't be capitalized.
no
No, but the names of individual languages are capitalized.
no
It should only be capitalized if it forms part of a title.
Yes... indeed it is!
No, it is a common noun.
No it is a common noun.
The word "not" is typically not capitalized in a title unless it is the first word, a proper noun, or part of a hyphenated word.
Mgnesium is sometimes referred to as "Mg."