Differentiate between:
$(i)$ Molar mass and Avogadro's constant.
$(ii)$ Molecular mass and formula unit mass.

$A$ gold sample contains $90\%$ of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

State whether the following statement is true or false:
$A$ mole always represents $6.023 \times 10^{22}$ atoms,molecules,or ions of a substance.

Give two examples to show that the law of conservation of mass applies to physical changes also.

Calculate the number of particles in each of the following:
$(a)$ $48 \,g$ of $Mg$
$(b)$ $8 \,g$ of $O_2$
$(c)$ $0.1$ mole of carbon (Atomic mass $Mg = 24 \,u, O = 16 \,u, C = 12 \,u$,Avogadro constant $= 6.022 \times 10^{23}$)

State three rules for writing the chemical formulae.