CHEMISTRY OXIDATION NUMBERS
please help me solve only 3 of those oxidation numbers

NO2
Cr2O72-
KCl
NH3
CaH2
SO42-
Na2O2
SiO2
CaCl2

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

If 90.0 grams of ethane reacted with excess chlorine,how many grams of dicarbon hexachloride would form

He table below gives the atomic mass and relative abundance values for the three isotopes of element m. relative abundance (%) atomic mass (amu) 78.99 23.9850 10.00 24.9858 11.01 25.9826 what is the average atomic mass (in amu) of element m? 2.86 5.36 24.30 24.98