What is the mass of :
$(a)$ $0.2$ mole of oxygen atoms?
$(b)$ $0.5$ mole of water molecules?

Which has more number of atoms,$100\,g$ of sodium or $100\,g$ of iron (given,atomic mass of $Na = 23\,u, Fe = 56\,u$)?

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

When $3.00 \,g$ of carbon is burnt in $8.00 \,g$ of oxygen,$11.00 \,g$ of carbon dioxide is produced. What mass of carbon dioxide will be formed when $3.00 \,g$ of carbon is burnt in $50.00 \,g$ of oxygen? Which law of chemical combination will govern your answer?

Convert the following into moles:
$(a)$ $12\, g$ of oxygen gas
$(b)$ $20\, g$ of water
$(c)$ $22\, g$ of carbon dioxide.

Which postulate of Dalton's atomic theory can explain the law of definite proportions?