What should you look for in a chemical formula to decide is a compound or element will not combust

You will look at its number lets say if you had H2O which is two hydrogen and one oxygen. The two hydrogen is combined with oxygen sharing it's electrons making it being covalent bonding. You need 8 valence electrons that meaning full outershell. Hydrogen only has one in it outershell oxygen has 6 that's what can make a compound

Answer is: A) solid.

There are five fundamental states of matter (gas, liquid, solid, plasma and Bose–Einstein condensate).  

In solid, molecules are closely packed, stiff and do not changes of shape or volume. Solid object (for example iron) does not take on the shape of its container.  

Liquids have definite volume, but no fixed shape.  

Gases (for example nitrogen and neon) not have definite volume and fixed shape, it depends on its container.  

Plasma is a an ionised gas with highly electrical conductivity.