If $10^{20}$ grains are distributed in one second,then the time taken to distribute an Avogadro number of grains is ........ hours.

Which of the following contains the maximum number of atoms?

How many moles of $Al_2(SO_4)_3$ are present in $50 \ g$ of the substance?

$A$ gaseous mixture of $O_2$ and $CH_4$ are in the ratio $1: 4$ by mass. Find the ratio of their molecules.

$A$ 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:

The number of water molecules in $250\, mL$ of water is closest to $.....\, \times 10^{23}$.
[Given: density of water is $1.0\, g\, mL^{-1}$; Avogadro's number $= 6.023 \times 10^{23}$]