Question

Iron is-useful metal​

Answer 1

No. You use the definite article hen you are talking about something specific. For example, you might say, “The iron used in that building is very strong.” If you are talking about iron in general as in your sentence, you do not use the definite article. You should say, “Iron is a useful metal.”

Answer 2

Explanation:

It is the most common chemical element on Earth (by mass), and the most widely used metal. It makes up much of the Earth's core, and is the fourth most common element in the Earth's crust. The metal is used a lot because it is strong and cheap. Iron is the main ingredient used to make steel.