Yes, it is a noun.
Yes, paper is a countable noun. It can be used in both singular and plural forms, such as "a piece of paper" or "several papers."
The term 'paper sheet' is a countable noun. The plural form is paper sheets.example: Nine paper sheets were attached to form one giant sheet.
Both. The use of the word paper for the substance on which you for example write, draw, or to wrap things is uncountable. Units of paper are expressed as sheets of paper, rolls of paper, stacks of paper, etc. The use of the word to describe an intellectual piece of work is countable.
It would be more appropriate to ask "How much paper" as paper is typically measured by weight or volume, rather than in countable units.
Stationery is considered a mass noun, which means it is typically uncountable. However, in certain contexts, it can be used as a countable noun when referring to individual items of stationery, such as pens, pencils, or notebooks. So, while stationery is generally uncountable, it can be treated as countable depending on how it is being referenced in a sentence.
countable
countable
The noun 'hill' is a countable noun. The plural form is 'hills'.
cookies are countable unless you have brain problems
countable
Shark is a countable noun.
Duck as an animal is countable, but if you mean the meat it is uncountable.