Which of the following elements will form acidic oxide?

The correct option is A

An element with atomic number $7$

Explanation for the correct option:

An acidic oxide is an oxide which produces acidic solution when we add water in it. Mostly non-metals form acidic oxide. So the element with atomic number $7$ will form acidic oxide because atomic no. $7$ element is Nitrogen and it is a non-metal.

Explanation for the incorrect options:

B) An element with atomic number $3$: An element with atomic number $3$ is Lithium which is not a non-metal, it is an alkali metal so it can’t form acidic oxide.

C) An element with atomic number $12$: An element with atomic number $12$ is Magnesium and it is a alkaline earth metal and not form acidic oxide.

D) An element with atomic number $19$: An element with atomic number $19$ is Potassium which is alkali metal and not form acidic oxide.

Hence option (A) is correct. Non-metals will form acidic oxide.