ANSWER: An orange, as in a fruit vs. the color orange, is a count noun (Purdue University OWL [https://owl.purdue.edu]. Count nouns are names for something that is countable and can form a plural, ie., boy/boys [a boy; the boys] orange/oranges [an orange; the oranges]
So, the correct answer is an orange. ...however:
"The" may precede a singular count noun (because we are talking about one orange fruit, so it is a singular count noun) that has a specific identity for the reader.
Example: The orange sitting on the table belongs to my sister, so don't take it.
I hope this helps. If you need more help as to why, read on below.
Try this: "RULES FOR "A" AND "AN" -- USE OF A/AN VS. THE"
It is crucial for an English learner that they grasp the proper use of all three common determiners (articles.) When/how to apply their use correctly. Be proficient in when to properly use all three of them. "A," "an," and "the" are the most common, but they are not all the determiners, either.
Determiners: Again, "a," "and," and "the" are called determiners and are the most common. They are special kinds of adjectives that mark nouns because they always come before them, and are also called "articles." Less common determiners (articles) include using "my," "their," "whose," "this," "these," "those," "one," "some," and "any."
Ref: Little Brown Handbook, 11th Ed. Pg. 322, Pearson Education, Inc. (2010).
RULES FOR A AND AN:
Use "a" before words beginning with consonant sounds (any letter of the alphabet other than the vowels, which are "a" "e" "i" "o" or "u.")
Examples: a truck; a water melon; a fire hose, etc. Each of these words begin with a consonant sound.
Use "a" as well for words spelled with an initial pronunciation sound of "h" and also include spelled with vowels that are sounded as consonants. Example: a historian, a one o'clock class ["one" sounds like "w" as in "won," so even though one starts with a vowel [o], it sounds like a consonant when pronounced, so use a. A university ["u" sounds like "you" which starts with "y' so use "a."
Use "an" that begin with vowels. Include consonants that have vowel sounds, including those spelled with an initial silent "h." [an organism,[organism has silent h] an L, [L when pronounced, sounds like the vowel "e."] an honor [honor has silent h, and sounds like vowel "o" when pronounced.]
Ref: Little Brown Handbook, 11th Ed., Pg. 865, Pearson Education, Inc. (2010)
Proper nouns: names of a person, place, or thing and begins with a capital letter: (Month, Holidays; ie., St. Valentines; July; Persons, cities or States/Country names Mr. John Smith, Columbus, Ohio; Africa, Canada, England.) Proper nouns are not preceded by determiners.
Count nouns: names for something that is countable and can form a plural, ie., boy/boys [a boy; the boys] orange/oranges [an orange; the oranges]
Noncount nouns: names something that is not usually considered countable in English, so does not form a plural, and sometimes require a determiner, such as: "air" [The air in Albequerque, NM is very dry.] "furniture" [I have furniture stored in the basement.] "wood"[Please put the wood over there.] - Human emotions, such as happiness, [There's so much happiness in the world why be sad?] anger,[John's anger is sometimes overwhelming.] joy, [The joy of planting a garden cannot be put into words.], etc.
RULES FOR A/AN VS. THE
Singular count nouns:
a. Use "a" or "an" with a singular count noun when you haven't let the reader know or are introducing it for the first time. [1. A dinosaur may have consumed as much as a crane bucket full of plant matter everyday. 2. An elephant has almost a two year gestation period, longer than any other mammal in the world.]
b. "The" precedes a singular count noun that has a specific identity for the reader for the following reasons:
- The author or writer mentioned it for the reader already.
- The author or writer identifies the single count noun either just before or after stating it.
- The author or writer mentions something where only one in the world exists, or is very unique (The George Washington University [[there's only one!]]
- The author or writer mentions a single count noun that is an institution or item shared across a community or large population. [The computer, the Internet, and the telephone all globally connect people from all over the earth.]
"The" is not used before singular nouns that are general or common - use "a" or "an;" but, use "the" when citing a specific instance, use "the." Examples: Such as for hurricanes, or fires, or disasters: [Common: 1. A hurricane swept through South Florida yesterday. 2. A house fire occurred this week. Specific: 1. The 1935 Labor Day Hurricane was the most intense hurricane on record for the United States, and The Galveston Hurricane of 1900 was the most deadliest. 3. The Great Chicago Fire, which burned for three days, left over 100,000 people homeless and occurred just before Winter in 1871.
With plural count nouns: A or an never precedes a plural noun. The does not precede a plural noun that names a general category. The does precede a plural noun that names specific representatives of a category. (Example: General category plural nouns: 1. Dogs and cats fight. Example: Plural noun that names specific representatives of a category: 1. The dogs living on Baker St., in the old abandoned house next to St. Michael's, were rounded up and impounded this morning.
With noncount nouns: "A" or "an" also never precede a noncount noun. "The" does precede a noncount noun when it names specific representatives of a general category.
(Example: Noncount noun [deforestation]: 1. Scientists say deforestation, this permanent destruction of forested land to make it available for other uses, affects global climate. Example 2: Noncount noun specific representative of a general category: [deforestation]: 1. The deforestation of Bolivia's Gran Chao is now at 85 percent completed in just the the last 30 years.
With proper nouns: "A or an never precedes a proper noun. The general doesn't, either, unless they are plural proper nouns. Example 1: proper noun: 1. Larry goes to work by bus each Tuesday. Example 2: plural proper noun: 1. The Johnsons moved to San Francisco last week, but Frank is still here cleaning their house.