The chemical symbol for sodium is

$(a)$ What is the law of constant proportions? Explain with the help of an example.
$(b)$ Which postulate of Dalton's atomic theory is in agreement with this law?

Calculate the mass of $10$ carbon atoms.

Which of the following represents a correct chemical formula? Name it.

$3.42 \, g$ of sucrose $(C_{12}H_{22}O_{11})$ is dissolved in $18 \, g$ of water $(H_2O)$. The number of oxygen atoms in the solution is:

$(i)$ Name the body which approves the nomenclature of elements and compounds.
$(ii)$ The symbol of sodium is written as $Na$ and not as $S$. Give reason.
$(iii)$ Name one element which forms diatomic and one which forms tetraatomic molecules.