ANS:A - sulphur

Red hot iron bend due to sulphur. When the iron is heated above it becomes red hot so the name given. At this temperature, it becomes malleable but due sulphur it becomes brittle & forms cracks due to grain heat concentration. Red-short, hot-short refers to brittleness of steels at red-hot temperatures. It is often caused by high sulfur levels, in which case it is also known as sulfur embrittlement. Red hot iron is otherwise know as hot metal (product from blast furnace) impurities in hot metal are:
Silica-imparts non-homoginity.
Carbon-brittleness.
Sulphur-surface cracks. This is due to the sulfur forming iron sulfide/iron mixtures in the grain boundaries of the metal which have a lower melting point than the steel.