The hardness of steel increases if it contains

Solution(By Examveda Team)

Martensite is a hard and brittle microstructure of steel that forms when steel is rapidly cooled from a temperature above the critical transformation temperature. The rapid cooling prevents the formation of other microstructures like pearlite, ferrite, or cementite, resulting in a high hardness.

Austenite (Option A) is the high-temperature phase of steel, which can transform into martensite upon rapid cooling. However, it is not inherently hard like martensite.
Pearlite (Option C) is a microstructure composed of alternating layers of ferrite and cementite. It does not contribute significantly to the hardness of steel.
Cementite (Option D) is a hard and brittle compound of iron and carbon, but it does not directly increase the hardness of steel when it is present in the microstructure.

Therefore, Option B: Martensite is the correct choice as it directly correlates with the increased hardness of steel.