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.

$(a)$ Write the chemical symbols of two elements:
$(i)$ which are formed from the first letter of the element's name.
$(ii)$ whose name has been taken from the names of the elements in Latin.
$(b)$ Define Avogadro's constant and molar mass. How are they related to one mole of an atom,molecule,or ion?

$(a)$ Calculate the number of moles in $112 \, g$ of iron.
$(b)$ Calculate the mass of $0.5$ mole of sugar $(C_{12}H_{22}O_{11})$.
$(c)$ Calculate the number of atoms in $8 \, g$ of oxygen $(O_2)$ molecules.
(Atomic mass of $Fe = 56 \, u, C = 12 \, u, H = 1 \, u, O = 16 \, u, N_A = 6.022 \times 10^{23} \, mol^{-1}$)

Which of the following correctly represents $360 \, g$ of water?
$(i)$ $2$ moles of $H_2O$
$(ii)$ $20$ moles of water
$(iii)$ $6.022 \times 10^{23}$ molecules of water
$(iv)$ $1.2044 \times 10^{25}$ molecules of water

$(a)$ 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: $H=1, O=16, N=14, Ca=40, Na=23$)