Q1.A compound of copper and sulphur is 65.43percent copper by mass.how many grams of copper can be obtained from 249g of this compound?and how many grams of sulphur remain?

Answer 1

Here is a worked example of a stoichiometry problem.
http://www.jiskha.com/science/chemistry/stoichiometry.html
But you can do it a lot faster another way.
249g copper sulfide x 0.6543 = g Cu that can be obtained.
S = 34.57 S and 249 x 0.3457 = g S in the 249 g.