Carl Wilhelm Scheele discovered several elements through chemical experiments including chlorine, oxygen, and nitrogen. He isolated chlorine by reacting manganese dioxide with hydrochloric acid and discovered oxygen by heating mercuric oxide, silver oxide, and nitre. Scheele also studied the rusting of iron and discovered that iron rusts in the presence of oxygen and water.

2. 
O, N, P, S, Cl, Br
C
Carl Wilhelm Scheele

3. 

4. 
S , O , Cl , Na , Mg , Al , C

5.  H
C N ,O ,S ,P
Fe3+ O2
Fe3+ CO(
Fe2+ O2
O2