An empirical formula: 1. gives the relative number of ions of each element per formula unit. 2. gives the number of ions of each element per formula unit. 3. uses lines to represent covalent bonds and shows how atoms in a molecule connect or bond to each other. 4. gives the relative number of atoms of each element per formula unit.5. gives the actual number of atoms of each element per formula unit.

4.  gives the relative number of atoms of each element per formula unit

Explanation:

An empirical formula -

It refers to the formula which determined the simplest whole - number ratio of all the atoms in a given species , is referred to as an empirical formula .

In simple terms ,

It is he smallest formula of the whole number which when multiplied by some whole number gives the actual structure of the compound .

Hence , from the given information of the question ,

The correct option for empirical formula is 4.

a electronegativity decreases beacuse the size of nucleus is bigger.