Calculate the molar mass of the following substances.
$(a)$ Ethyne,$(C_2H_2)$
$(b)$ Sulphur molecule,$(S_8)$

Calculate the number of molecules of sulphur $(S_8)$ present in $16 \, g$ of solid sulphur.

Define formula unit mass of a compound. Calculate the formula unit mass of:
$(a)$ $Na_{2}CO_{3} \cdot 10H_{2}O$
$(b)$ $CuSO_{4}$
(Given atomic mass of $Na = 23 \text{ u}, C = 12 \text{ u}, O = 16 \text{ u}, Cu = 63.5 \text{ u}, S = 32 \text{ u}, H = 1 \text{ u}$)

$A$ silver ornament of mass $m \, g$ is polished with gold equivalent to $1\%$ of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.

Verify by calculating that:
$(a)$ $5 \, mol$ of $CO_2$ and $5 \, mol$ of $H_2O$ do not have the same mass.
$(b)$ $240 \, g$ of calcium and $240 \, g$ of magnesium elements have a mole ratio of $3:5$.

What is the fraction of the mass of water due to neutrons?