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

Calculate the molecular masses of $H_2$,$O_2$ and $Cl_2$.

Write down the names of compounds represented by the following formulae:
$(i) Al_{2}(SO_{4})_{3}$
$(ii) CaCl_{2}$
$(iii) K_{2}SO_{4}$
$(iv) KNO_{3}$
$(v) CaCO_{3}$

What is meant by the term chemical formula?

Calculate the molecular masses of $C_2H_4$,$NH_3$ and $CH_3OH$.

In a reaction,$5.3 \, g$ of sodium carbonate reacted with $6 \, g$ of acetic acid. The products were $2.2 \, g$ of carbon dioxide,$0.9 \, g$ of water,and $8.2 \, g$ of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.
$\text{Sodium carbonate} + \text{Acetic acid} \to \text{Sodium acetate} + \text{Carbon dioxide} + \text{Water}$