Question

An element that burns spontaneously in air:

• A. Sulphur
• B. Carbon
• C. Phosphorous
• D. Magnesium

Answer 1

The correct option is C

Phosphorous

Explanation of correct option:

C. Phosphorous (P)

• Phosphorous has an atomic number of 15 and it lies in the 15^th group and 2^nd period of the modern periodic table.
• Phosphorous has a very low ignition temperature (lower than the room temperature) so, it burns rapidly in the air at room temperature.
• The ignition temperature of a substance is the minimum temperature at which the substance catches fire for spontaneous combustion.
• Phosphorous is mainly of two types-

1. White Phosphorous
2. Red Phosphorous

Explanation of incorrect options

A. Sulfur (S)

• Sulfur (S) has atomic number of 16 and it lies in 16^th group and 2^nd period of modern periodic table .
• Sulfur is a low reactive nonmetal.
• Thus, it does not catch fire easily

B. Carbon (C)

• Carbon (C) has an atomic number of 6 and it lies in the 14^th group and 2^nd period of the modern periodic table .
• Carbon is generally present in all organic compounds.
• Even Carbon dioxide is used in fire extinguishers to stop the fire.

D. Magnesium (Mg)

• Magnesium (Mg) has atomic number of 12 and it lies in 2^nd group and 2^nd period of modern periodic table .
• Magnesium is a moderately reactive metal, which does not catch fire easily.
• Magnesium ribbon on burning gives white dazzling flame.

Hence, option (C) is correct, i.e. Phosphorous burns rapidly in air at room temperature.