What is the oxidation number of chromium in dichromate ion, cr2o72-?

Matches the chemical name of each oxide of phosphorus to its chemical formula

2. how is heavy water different from normal water

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