$A$ mixture of hydrogen and oxygen contains $20\%$ by weight of hydrogen. Find the total number of molecules per gram of the mixture.

What are the different elements present in the mineral barite?

Blue vitriol is

When $1 \ L$ of $N/5 \ HCl$ aqueous solution in a beaker is boiled,the volume of the resulting solution becomes $250 \ mL$. During this process,$3.65 \ g$ of $HCl$ is lost. What will be the concentration of the resulting solution? $(HCl = 36.5 \ g/mol)$

$100 \ mL$,$1 \ M$ $H_2SO_4$ solution of density $1.5 \ g/mL$ is mixed with $400 \ mL$ of water,resulting in a diluted solution of density $1.25 \ g/mL$. Find the molarity of the final diluted solution. (Density of water $= 1 \ g/mL$)

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 ....... $kJ \ mol^{-1}$