Q.When CaC₂ is heated in atmospheric nitrogen in an electric furnace the compound formed is

Burning Mg in air gives mainly white MgO (with the characteristic brilliant white flame) plus a small amount of Mg₃N₂ from reaction with atmospheric nitrogen.

Air is mainly a mixture of O₂ (~21%) and N₂ (~78%). Magnesium, being a fairly reactive s-block (alkaline earth) metal, reacts with both gases when ignited:

1. Reaction with oxygen (the major reaction):

   2Mg(s) + O₂(g) → 2MgO(s)

   This reaction is highly exothermic and produces an intense, dazzling white light — this is why magnesium ribbon is used in fireworks/flash photography/flares. The product MgO is a white powdery solid (basic oxide).

2. Reaction with nitrogen (a minor, simultaneous reaction):

   3Mg(s) + N₂(g) → Mg₃N₂(s) (magnesium nitride)

   …