The relative atomic mass of an oxygen atom is $16$. Explain its meaning.

In a compound such as water,the ratio of the mass of hydrogen to the mass of oxygen is always

State whether the following statement is true or false:
The atomicity of phosphorus is $5$ and that of sulphur is $6$.

State whether the following statement is true or false:
Mass of two moles of atoms or molecules is called molar mass.

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 $Na = 23 \text{ u}, C = 12 \text{ u}, O = 16 \text{ u}, Cu = 63.5 \text{ u}, S = 32 \text{ u}, H = 1 \text{ u}$)

In photosynthesis,$6$ molecules of carbon dioxide combine with an equal number of water molecules through a complex series of reactions to give a molecule of glucose having a molecular formula $C_6H_{12}O_6$. How many grams of water would be required to produce $18\, g$ of glucose? Compute the volume of water (in $cm^3$) so consumed assuming the density of water to be $1\, g\, cm^{-3}$.