Answer: Because more energy is required to form
ion.
Step-by-step explanation:
Oxygen is the 8th element of the periodic table which belongs to Group 16.
The electronic configuration of the element is:
![1s^22s^22p^4](https://img.qammunity.org/2020/formulas/chemistry/middle-school/rnpl8dbr8topswjtty6vgfawasfrwl0cig.png)
The number of valence electrons are 6 which is not a stable electronic configuration.
To attain stable electronic configuration, this element will either loose 6 electrons to form
ion or gain 2 electrons to form
ion.
The loosing of 6 electrons require a huge amount of energy and is an unfavorable reaction. Hence, this element will gain 2 electrons easily and form
ion.
This element is considered as a non-metal because it gains electron to attain stable electronic configuration.