Calcium Nitrate is the substance that gives a brick red flame and breaks down on heating, giving oxygen and brown gas.

Here's a detailed explanation:

Brick Red Flame:
Calcium nitrate is a compound that contains calcium and nitrate ions. When heated, the calcium ions in the compound get excited and emit energy in the form of visible light. The specific arrangement of electrons in the calcium ions causes the emission of a brick red flame.

Breaks Down on Heating:
When calcium nitrate is heated, it undergoes decomposition. The heat energy supplied provides the activation energy required for the reaction to occur. The decomposition of calcium nitrate results in the production of calcium oxide (CaO), nitrogen dioxide gas (NO2), and oxygen gas (O2).

The balanced equation for the decomposition reaction is:
2Ca(NO3)2(s) → 2CaO(s) + 4NO2(g) + O2(g)

Formation of Oxygen and Brown Gas:
During the decomposition of calcium nitrate, one of the products formed is oxygen gas (O2). Oxygen is released as a result of the breakdown of the nitrate ions (NO3-) in the compound. The oxygen gas released supports combustion and can be observed as it reignites a glowing splint.

The brown gas produced during the decomposition of calcium nitrate is nitrogen dioxide (NO2). Nitrogen dioxide is a reddish-brown gas that is formed due to the reaction between nitrogen oxide (NO) and oxygen gas (O2) in the air. It is highly toxic and has a pungent odor.

Overall, the decomposition of calcium nitrate on heating produces oxygen gas and brown nitrogen dioxide gas, along with calcium oxide.

In conclusion, calcium nitrate is the substance that exhibits a brick red flame and breaks down on heating, giving oxygen gas and brown nitrogen dioxide gas.