A substance which gives brick red flame and breaks down on heating to give oxygen and a brown gas is

1. Magnesium nitrate

2. Calcium nitrate

3. Barium nitrate

4. Strontium nitrate

Hint:  Calcium compound give red colour on heating

Calcium gives brick red coloured flame. Hence, calcium nitrate on heating decomposes into calcium oxide, with the evolution of a mixture of NO2 and O2.
2 Ca(NO3)2 → 2 CaO + NO2 + O2
NO2 is brown coloured gas.

Barium nitrate gives Green colour on heating.
Magnesium nitrate gives no colour.
Strontium nitrate gives crimson red.