Thermal decomposition yielding NO2 for PAN formation

Steps:

• PAN forms via NO2 reaction with peroxyacetyl radicals from unburned hydrocarbons in photochemical smog.
• Gas M is thus NO2, requiring L to release NO2 on heating.
• Eliminate C: MgCO3 decomposes to MgO + CO2; CO2 does not form PAN.
• Confirm B: Ca(NO2)2 decomposes to CaO + NO + NO2, producing NO2.

Why B is correct:

• Ca(NO2)2 decomposes on heating to yield NO2 gas, which directly reacts with oxidized hydrocarbons to produce PAN per atmospheric chemistry.

Why the others are wrong:

• A. Ca(NO3)2 is a nitrate that decomposes to NO2 + O2, but the intended compound is the nitrite for selective NO2 production without excess oxygen.
• C. MgCO3 decomposes to CO2, which plays no role in PAN formation.
• D. Mg(NO2)2 decomposes similarly to nitrites but is unstable and typically yields NO primarily, not sufficient NO2 for PAN.

Final answer: B