Do $5$ moles of $CO_{2}$ and $5$ moles of $H_{2}O$ have the same mass?

$A$ gold sample contains $90\%$ of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

Name the international organization that approves the names of elements. Give an example with an explanation to show that the Law of Conservation of Mass applies to physical changes as well.

Which of the following correctly represents $360 \,g$ of water?

State the number of atoms present in each of the following chemical species:
$(a)$ $CO_{3}^{2-}$
$(b)$ $PO_{4}^{3-}$
$(c)$ $P_{2}O_{5}$
$(d)$ $CO$

$(a)$ 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?