$K_2CS_3$ is called potassium ...... .

If $10^{21}$ molecules are removed from $100 \, mg$ of $CO_2$,how many moles of $CO_2$ remain?

Arrange the following in the order of increasing mass (atomic mass: $O = 16, Cu = 63, N = 14$)
$I.$ one atom of oxygen
$II.$ one atom of nitrogen
$III.$ $1 \times 10^{-10}$ mole of oxygen
$IV.$ $1 \times 10^{-10}$ mole of copper

$(i)$ Calculate the total number of electrons present in one mole of methane.
$(ii)$ Find $(a)$ the total number and $(b)$ the total mass of neutrons in $7 \, mg$ of $^{14}C$. (Assume that mass of a neutron $= 1.675 \times 10^{-27} \, kg$).
$(iii)$ Find $(a)$ the total number and $(b)$ the total mass of protons in $34 \, mg$ of $NH_3$. Will the answer change if the temperature and pressure are changed?

Lattice enthalpy and enthalpy of solution of $NaCl$ are $788 \ kJ \ mol^{-1}$ and $4 \ kJ \ mol^{-1}$ respectively. The hydration enthalpy of $NaCl$ is ....... $kJ \ mol^{-1}$

Which of the following has the maximum mass?