Answer:
HgO (empirical formula)
Explanation:
4.08 - 3.78 = 0.3g (oxygen)

0.02 : 0.02
0.02/0.02 : 0.02/0.02
1 : 1 (ratio)
HgO ( empirical formula)
2HgO ----> 2Hg + O2 ( your equation correct)
Most elements on group 18 are the Noble Gases. They already have a complete last level with 8 electrones. Actually they can form compounds but only on the lab and they will not even last half a second.
Answer: S8(s) + 8O2(g) → 8SO2(g) ΔH = -2368 kJ a.