Two different alkali metals M₁ and M₂ form nitrates M₁ NO ₃ and M₂ NO ₃ . Upon strong heating, M₁ NO ₃ evolves a brown gas along with a colourless gas, whereas M₂ NO ₃ evolves only a colourless gas. Identify M₁ and M₂ from the given options.

Step-by-step solution

Alkali metal nitrates decompose on heating. Except lithium, all other alkali metal nitrates decompose to give the corresponding metal nitrite and oxygen (a colourless gas). 2M NO ₃ 2M NO ₂ + O ₂ (where M = Na, K, Rb, Cs ) Lithium nitrate exhibits anomalous behaviour and decomposes to give lithium oxide, nitrogen dioxide (a brown gas), and oxygen (a colourless gas). 4 LiNO ₃ 2 Li ₂ O + 4 NO ₂ + O ₂ Since M₁ NO ₃ evolves a brown gas, M₁ must be Li . Since M₂ NO ₃ evolves only a colourless gas, M₂ can be Na , K , Rb ,