Identify the symbol used for water according to $\text{Dalton's}$ atomic theory?

Which of the following pairs of substances illustrate the law of multiple proportions?

The statement related to the law of definite proportions is:

$A$ sample of calcium carbonate has the following percentage composition: $Ca = 40 \%$,$C = 12 \%$,and $O = 48 \%$. According to the law of definite proportion,the weight of calcium in $4 \ g$ of a sample of calcium carbonate from another source will be (atomic weights: $Ca = 40, C = 12, O = 16$).

Which of the following pairs of compounds demonstrates the law of multiple proportions?

Explain Dalton's atomic theory.