When magnesium is added to copper sulphate the liquid turns to what?
I presume that, by “the liquid”, you mean copper sulphate solution. If so, the liquid will slowly turn from blue to colourless: you’ll finish up with a solution of magnesium sulphate and the copper will precipitate out as a brown powder. Chemically, what will have happened is that magnesium, being more electropositive than copper, will displace the copper.