Concept:Burning of magnesium in air is an exothermic combustion reaction that releases energy in the form of visible light and heat.
Explanation:When a magnesium ribbon is ignited, it reacts rapidly with oxygen present in air.
The reaction is:
2Mg+O2→2MgO.
This reaction produces magnesium oxide and releases chemical energy.
The energy is given out partly as heat and partly as intense white light.
The characteristic dazzling white flame observed during this process confirms the emission of light energy.
At the same time, a large amount of heat is liberated, so the resulting ash becomes very hot.
No sound is evolved during the normal burning of magnesium in air.
Therefore, the energy evolved is in the form of both light and heat, not sound or heat only.
Answer:C. light and heat