The correct procedure of heating iron-sulphur mixture to prepare iron sulphide is :
A. heat the powder mixture at the base of the test tube using a blue flame throughout
B. heat the iron filings and sulphur mixture in the middle of the test tube using yellow flame throughout
C. heat the powder mixture at the top of the test tube using an orange flame throughout
D. heat the iron filings-sulphur mixture at 3/4 quarters of the test tube using a red flame throughout.
