Which of the following when used in ordinary low carbon steels, makes the metal ductile and of good bending qualities?

Answer: Option C

It is a mild deoxidant acting as a cleanser taking the sulphur and oxygen out of the melt into the slag.
It increases the harden ability and tensile strength but decreases ductility.
It combines with sulphur to form globular manganese sulphides, essential in free cutting steels for good machinability.