Calculate the number of moles present in $9.10 \times 10^{-2} \ kg$ of water.

$138 \ g$ of ethyl alcohol is mixed with $72 \ g$ of water. The ratio of mole fraction of alcohol to water is

The mass of $112 \ cm^3$ of $CH_4$ gas at $STP$ is ............. $g$.

$K-40$ is a natural radioactive isotope which constitutes $0.012\%$ of natural potassium. If a cup of milk contains $370 \ mg$ of $K$,how many atoms of $K-40$ are ingested?

The number of moles of water present in a spherical water droplet of radius $1.0 \ cm$ is,(Given: Density of water in the droplet $= 1.0 \ g \ cm^{-3}$)

The number of electrons in $2.1 \ g$-ion of $Cl^{-}$ is