Which era did we live on in 2008

Ineed with my science work! it’s due tomorrow!

Zoe is investigating the composition of substance a, an unknown substance. using chemical processes, she analyzes substance a and determines it is composed of sodium, oxygen, and hydrogen atoms in a ratio of 1 : 1 : 1. what is substance a? a. a compound b. an element c. a heterogeneous mixture d. a homogeneous mixture

Will mark brainliest how many electrons can be held in the energy level n = 4?