Which of the following bricks are used for lining of furnaces? A. Over-burnt bricks B. Under-burnt bricks C. Refractory bricks D. First class bricks

The correct answer is C. Refractory bricks.

Refractory bricks are used for lining furnaces because they are able to withstand high temperatures without melting or cracking. They are made from materials such as fireclay, silica, and alumina, which are all resistant to heat.

Over-burnt bricks are bricks that have been fired at too high a temperature. This can cause them to become brittle and crack.

Under-burnt bricks are bricks that

First class bricks are bricks that meet the highest standards of quality. They are made from high-quality materials and are carefully fired to ensure that they are strong and durable.

However, first class bricks are not necessarily the best type of brick to use for lining furnaces. Refractory bricks are specifically designed to withstand high temperatures, and they are therefore the best choice for this application.