Which of the following chemical formulas could represent a stable compound formed with an element "X" from group 1A and Oxygen?

1. XO

2. X2O

3. X2O2

4. X3O

2. X₂O

Explanation:

Elements in group 1A are known as alkali metal. Examples include lithium, sodium, and potassium among others. These elements have one valence electron in the outermost energy level and therefore form cations with a charge of + 1. They have a valency of 2. Oxygen, on the other hand, has a valency of 2. Therefore, a chemical formula of a compound formed when an element in group 1A say X reacts with oxygen will be X₂O. To write the formula, we identify the symbol of the elements and their valence. Then the atoms of the two elements exchange their valencies which are written as a subscript on each symbol of an element.