Decomposition of calcium nitrate yields brown NO2 and O2

Steps:

• Recall the thermal decomposition reaction: 2Ca(NO3)2 → 2CaO + 4NO2 + O2.
• Identify NO2 as a brown gas produced.
• Note O2 enables the glowing splint to relight.
• Match to option B: brown gas with splint relighting.

Why B is correct:

• The reaction formula confirms brown NO2 gas and O2, where O2 supports combustion, relighting the splint per oxygen test definition.

Why the others are wrong:

• A: Brown gas correct, but splint relights in O2, not goes out.
• C: Gas is brown, not colourless; splint relights, not goes out.
• D: Gas is brown, not colourless.

Final answer: B