The correct answer is D. no article.
The word “honest” is an adjective that describes a person who is truthful and fair. It is not a proper noun, so it does not need an article.
The other options are incorrect because they are all articles. An article is a word that is used to introduce a noun or noun phrase. The articles “a” and “an” are used before singular nouns that begin with a consonant sound, while the article “the” is used before singular nouns that begin with a vowel sound or a consonant sound that is pronounced as a vowel.
In the sentence “Harishchandra was an honest king,” the article “an” is used before the noun “king” because the word “king” begins with a consonant sound. However, in the sentence “Harishchandra was honest,” the word “honest” is an adjective that describes the noun “king,” so it does not need an article.