$3.42 \, g$ of sucrose are dissolved in $18 \, g$ of water in a beaker. The number of oxygen atoms in the solution are

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

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

$A$ $0.24 \, g$ 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.

$(a)$ What are molecules? Using examples, differentiate between the molecules of an element and a compound.
$(b)$ Derive the chemical formulae of the molecules formed between the following ions:
$(i)$ $Al^{3+}$ and $SO_{4}^{2-}$
$(ii)$ $Ba^{2+}$ and $NO_{3}^{-}$

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