2A + O₂ → 2AO

a/24 ← a/48

Gọi a là m_A

⇒ mO₂ = 2/3a (g)

nO₂= 2/3a : 32 = a/48 (mol)

MA = a : a/24 = 24(g/mol)

vậy A là Mg

2KClO₃ → 2KCl + 3O₂

a/122,5 → a/735

2KMnO₄ → K₂MnO₄ + MnO₂ + O₂

b/158 → b/158

nKClO₃ = a/122,5 (mol)

nKMnO₄= b/ 158 (mol)

theo đề: mO₂₍₁₎=mO₂₍₂₎

⇔ a/735 = b/ 158

⇔ a/b= 158/735