Explain, why diamond is considered as an element, not as a compound?

Round up the following upto three significant figures.

$10.4107$

$32 \mathrm{g}$ of sulphur reacts with $32 \mathrm{g}$ of oxygen even if more than $32 \mathrm{g}$ of sulphur are available. Which law of chemical combination does this illustrate?

Give the empirical formula of the following substance. 

${\mathrm{C}}_6{\mathrm{H}}_6$

Give the empirical formula of the following substance. 

Graphite

Give the empirical formula of the following substance. 

Magnesium chloride