The 4 second rule is used to estimate your total stopping distance under ideal conditions.
The units of density are g/ml. If you find the grams of 1 mol of ethanol (with the molecular weight), you can then divide by the density to get the ml of ethanol.
g*(ml/g)=ml
Answer: When an iron nail immersed in the solution of copper sulphate than iron displaces copper from the solution of copper sulphate because iron is more reactive than copper. Therefore copper sulphate solution colour changes from blue to pale green.