Question

please help
2. Which of these chemical formulas NaCl, O2, He, or SO2 represents both an element and a molecule?

NaCl

O2

He

SO2


4. Which subatomic particles have approximately the same mass?

protons and electrons

neutrons and electrons

protons and neutrons

electrons and atoms


13. Which of the following represents an incorrectly balanced chemical equation? (Points : 5)

Na2CO3 (s) Na2O (s) + CO2 (g)
Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)
2ZnS (s) + 2HCl (aq) 4ZnCl2 (aq) + H2S (g)
4Al (s) + 3O2 (g) 2Al2O3 (s)