how iron sulphide is formed
My -- your school is teaching chemistry at a very young age!
Since this is not my area of expertise, I searched Google under the key words "iron sulphide form" to get this source:
http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/elements_com_mix_3.shtml
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.