Explain the following  :

(i) Law of conservation of mass  (ii) Gram atomic mass

(iii) Gram molecular mass.

The mass of copper oxide obtained by reacting $2.16 \mathrm{g}$ of metallic copper with nitric acid followed by strong heating was found to be $2.7 \mathrm{g}$. In another experiment, $1.15 \mathrm{g}$ of copper oxide on reduction yielded $0.92 \mathrm{g}$ of copper. Show that this data illustrates the law of constant composition.

What is the necessity of mole? Describe gram atomic mass and gram molar mass in terms of mole concept. Give one example in each case to support your answer.

What weight of calcium will contain the same number of atoms as are present in $3.2 \mathrm{g}$ of sulphur?