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

$1 \, L$ aqueous solution of $H_{2}SO_{4}$ contains $0.02 \, mmol$ $H_{2}SO_{4}$. $50 \%$ of this solution is diluted with deionized water to give $1 \, L$ solution $(A)$. In solution $(A)$,$0.01 \, mmol$ of $H_{2}SO_{4}$ are added. Total $mmol$ of $H_{2}SO_{4}$ in the final solution is $...... \times 10^{-3} \, mmol$.

Which of the following formulas is correctly represented according to Stock notation?

An organic compound contains $46.78 \%$ of a halogen $X$. When $2.00 \ g$ of this compound is heated with fuming $HNO_3$ in the presence of $AgNO_3$,$2.21 \ g$ of $AgX$ is formed. The halogen $X$ is:
[Given: atomic weight of $Ag = 108, F = 19, Cl = 35.5, Br = 80, I = 127$]

$A$ metal oxide contains $75 \%$ metal by mass. If the vapour density of the metal chloride is $89$,what is the atomic weight of the metal?

$(i)$ 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?