Which compound is formed when iron reacts with carbon?

Which of the following is the correct formula for a compound of scandium and oxygen?

Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with:
$(i)$ iodide
$(ii)$ iron $(II)$ solution and
$(iii)$ $H_{2}S$

Thermal decomposition of a $Mn$ compound $(X)$ at $513 \ K$ results in compound $Y$,$MnO_2$ and a gaseous product. $MnO_2$ reacts with $NaCl$ and concentrated $H_2SO_4$ to give a pungent gas $Z$. Identify $X, Y$ and $Z$.

What is the starting material for the preparation of $KMnO_4$?

Which of the following elements is doped into a fiber amplifier in an optical fiber communication system?