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

Assign $A, B, C, D$ from the given type of reaction.
$CaCl_2 + Na_2SO_4 \longrightarrow $ No reaction

$50 \ mL$ of $10 \ N \ H_2SO_4$,$25 \ mL$ of $12 \ N \ HCl$,and $40 \ mL$ of $5 \ N \ HNO_3$ were mixed together,and the volume of the mixture was made $1000 \ mL$ by adding water. The normality of the resultant solution will be.....$N$.

$3.0$ molal $NaOH$ solution has a density of $1.110 \, g/mL$. The molarity of the solution is

$(i)$ 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?

What is the percentage of lead in a lead pencil (in $\%$)?