Copper is _________ useful metal.
Copper is _________ useful metal.
Explanation
Article (a,an,the) are used before a noun.
A & An are called Indefinite Article.
We use a when there is Consonant sound.
We use an when there is vowel sound.
Useful gives consonant sound.
Wrong: Copper is an useful metal.
Right: Copper is a useful metal تانبا ایک مفید دھات ہے