You are provided with a fine white-coloured powder which is either sugar or salt. How would you identify it without tasting?

$(i)$ $(a)$ What do you understand by $1 \text{ amu}$ or $1 \text{ u}$?
$(b)$ How is it linked with relative atomic mass?
$(ii)$ How do we know the presence of atoms if they do not exist independently for most of the elements?

Which amongst the following has a greater number of atoms,$11.5 \, g$ of sodium $(Na)$ or $15 \, g$ of calcium $(Ca)$? How? (Given: atomic mass of $Na = 23 \, u$,$Ca = 40 \, u$)

$(a)$ Calculate the number of moles in $112 \, g$ of iron.
$(b)$ Calculate the mass of $0.5$ mole of sugar $(C_{12}H_{22}O_{11})$.
$(c)$ Calculate the number of atoms in $8 \, g$ of oxygen $(O_2)$ molecules.
(Atomic mass of $Fe = 56 \, u, C = 12 \, u, H = 1 \, u, O = 16 \, u, N_A = 6.022 \times 10^{23} \, mol^{-1}$)

What is the difference between $2H$ and $H_2$?

Which has more number of atoms?
$(i)$ $100 \, g$ of $N_2$
$(ii)$ $100 \, g$ of $NH_3$