What is the total number of carbon atoms present in $n$ mole of citric acid (in $n$)?

$A$ sample of ammonium phosphate,$(NH_4)_3PO_4$,contains $6$ moles of hydrogen atoms. The number of moles of oxygen atoms in the sample is:

How many moles of $BaCO_3$ will contain $1.5$ moles of oxygen atoms?

Volume occupied by one molecule of water (density $= 1 \ g \ cm^{-3}$) is ...... $ \times 10^{-23} \ cm^3$.

The mass and volume of $1/4$ mole of oxygen gas at $STP$ are respectively .....

Which one of the following will have the largest number of atoms?
$(i)$ $1 \,g$ $Au_{(s)}$
$(ii)$ $1 \,g$ $Na_{(s)}$
$(iii)$ $1 \,g$ $Li_{(s)}$
$(iv)$ $1 \,g$ of $Cl_{2(g)}$