The coal with the highest energy available per unit burned is

Anthracite

Explanation:

Anthracite variety of coal is the coal with the highest energy available per unit burned. Anthracite is hard, brittle, lustrous coal . They also often referred as hard coal. Anthracite has a high percentage of carbon and low percentage of volatile matter. Other varieties of coal  are peat, lignite and bituminous.  

1 a

2 d

3 a

4 c

explanation:

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a