Which type of chemistry studies the chemical reactions that occur in the human body?

Is this a single replacement reaction or there is no

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

Why is the melting of ice a physical change ?