$A$ $0.24 \, g$ sample of a compound of oxygen and boron was found by analysis to contain $0.096 \, g$ of boron and $0.144 \, g$ of oxygen. Calculate the percentage composition of the compound by weight.

$(a)$ Calculate the percentage of oxygen in $H_{2}O_{2}$.
$(b)$ Calculate the number of moles in $56 \, g$ of nitrogen gas $(N_{2})$.
$(c)$ Calculate the mass of $0.50$ moles of $Ca$ atoms.
$(d)$ Find out the number of particles in:
$(i)$ $5$ moles of methane gas $(CH_{4})$
$(ii)$ $92 \, g$ of sodium $(Na)$
(Atomic masses: $H=1, O=16, N=14, Ca=40, Na=23$)

$A$ molecule can be defined as the

Write the chemical formulae for the following substances and calculate the molecular mass for each one of them:
$(a)$ Caustic potash
$(b)$ Baking soda
$(c)$ Limestone
$(d)$ Caustic soda
$(e)$ Ethanol
$(f)$ Common salt

Carbon-containing molecules present in all life forms include:

State the postulate of Dalton's atomic theory which led to the law of conservation of mass. Calculate the molecular mass of water.