Which of the following would have to gain two electrons in order to achieve a noble gas electron configuration?

O

Sr

Na

Se

Br

The answer to your question is: Oxygen (O) and Selenium (Se)

Explanation:

Elements located in group VIA needs to gain 2 electrons to achieve noble gas electron configuration.

Oxygen (O) is located in group VIA so it needs to gain two electrons to become stable.

Strontium (Sr) is located in group IIA so it needs to lose 2 electrons to become stable.

Sodium (Na) is located in group IA so it needs to lose one electron to become stable.

Selenium (Se) is located in group VIA so it needs to gain 2 electrons to become stable.

Bromine (Br) is located in group VIIA so it needs to gain one electron to become stable.