Write the names of the compounds represented by the following chemical formulae:
$(i)$ $NaBr$
$(ii)$ $Al_{2}O_{3}$
$(iii)$ $Zn(NO_{3})_{2}$
$(iv)$ $HCl$
$(v)$ $NaCl$
$(vi)$ $CaCO_{3}$

Which of the following contains the maximum number of molecules?

Which of the following has the maximum number of atoms?

$A$ sample of vitamin $C$ is known to contain $2.58 \times 10^{24}$ oxygen atoms. How many moles of oxygen atoms are present in the sample?

Fill in the missing data in the Table.

Species property	$H_2O$	$CO_2$	$Na$ atom	$MgCl_2$
No. of moles	$2$	-	-	$0.5$
No. of particles	-	$3.011 \times 10^{23}$	-	-
Mass	$36 \, g$	-	$115 \, g$	-

$(a)$ Calculate the mass of $0.5$ mole of oxygen atoms.
$(b)$ Calculate the number of molecules of glucose present in its $90 \ g$ (molecular mass of glucose is $180 \ u$). (Avogadro constant $= 6.022 \times 10^{23} \ mol^{-1}$)
$(c)$ Calculate the number of moles of water in $2 \ g$ of water.
(Atomic mass of $H = 1 \ u, O = 16 \ u$)