Question

Which of the following non-metals reacts and catches fire on
exposure to air?
(a) phosphorus (c) sulphur
(b) nitrogen (d) hydrogen


NCERT Class VIII
Science - Exemplar Problems

Chapter 4. Materials: Metals and Non-Metals

Answer 1

option - a   is the correct answer

Answer 2

Phosphorous catches fire when exposed to air.

Answer - (Option A)

Explanation:

• Phosphorous catches fire when exposed to air. White phosphorous burns and catches fire in air spontaneously and combines with oxygen in the air and oxidizes to form phosphorous pentoxide.
• Phosphorous is highly reactive in air and gets ignited spontaneously even in moist air at $30^oC$.
• So to prevent its spontaneous reaction in air, it is often kept in water.
• The reaction is highly exothermic and releases high energy that it produces a yellow flame with white smoke.
• It is for this property of phosphorous to set off the fire when exposed in air, it is used in Military to ignite the munitions.