Formation of heat and/or light when two substances are combined indicate a change.

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

The same side of the moon always faces earth because the

Which radioisotope is used to date fossils? a. oxygen-16 b. carbon-14 c. uranium-238 d. carbon-12