Yes
The noun 'oranges' is the plural form for the noun orange, a common, concrete noun; a word for a thing.
There is no specific collective noun for mandarin oranges, in which case a noun that suits the situation is used, for example, a bag of mandarin oranges, a box of mandarin oranges, a bushel of mandarin oranges, etc.
There is no standard collective noun for oranges, in which case a noun that suits the situation is used, for example, a bagof oranges, a box of oranges, a crate of oranges, etc.
Yes one orange, three oranges
Yes, "orange juice" is a common noun. It refers to a type of beverage made from oranges and is not the name of a specific brand or product. Common nouns denote general items or concepts, while proper nouns identify specific names. Thus, "orange juice" fits the definition of a common noun.
Is orange a concrete
In the sentnece, "You have an orange.", the count noun is orange. In this sentence, it is just one orange (indicated by the article 'an'), but it could be two oranges, or many oranges.
Common noun
common
Pea is a common noun, and peas is the plural...still a common noun.
A common noun.
Most definitely a common noun.