Cathode Ray experiment to figure out electrons exist -> atoms can be broken up into subatomic particles
What dont u understand about lewis dot structures???.
.how to determine the number of dots ..or
Explanation:
elements are based on electrical conductivity
Answer: Compound
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper 
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water 

Thus as it give that the red sample on being heated, a gas is released and a blue powder is left after the heating. Thus the given sample is a compound.