Chemical or physical change? and what made you think such?

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

An atom of which element reacts with an atom of hydrogen to form a bond with the greatest degree of polarity ?

Write a balanced equation showing the formation of copper (ii) nitrite from its elements