Which formula equation shows a reversible reaction

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

Select all of the methods through which a drug can enter your body. injection swallowing inhalation absorption

How many valence electrons are in atom of radon?