The correct answer is: none of the above.
The word “ant” is a common noun, which means that it does not refer to a specific ant. Therefore, we do not need to use an article (a, an, or the) before it.
The article “a” is used before singular common nouns that refer to something that is not specific. For example, we might say “I saw a dog” to refer to any dog.
The article “an” is used before singular common nouns that begin with a vowel sound. For example, we might say “I saw an elephant” to refer to any elephant.
The article “the” is used before singular common nouns that refer to a specific thing. For example, we might say “I saw the elephant that escaped from the zoo” to refer to a specific elephant.
In the sentence “How much weight can ant carry?”, the word “ant” is not referring to a specific ant, so we do not need to use an article.