Which from following gases of same mass exerts highest pressure at constant temperature?

Calculate the volume of unit cell of an element having molar mass $27 \mathrm{~g} \mathrm{~mol}^{-1}$ that forms fcc unit cell. $\left[\rho . \mathrm{N}_{\mathrm{A}}=16.0 \times 10^{23} \mathrm{~g} \mathrm{~cm}^{-3} \mathrm{~mol}^{-1}\right]$

What is the ratio of concentration of salt to concentration of weak acid in buffer solution to maintain its pH value $7.2\left(\mathrm{pK}_{\mathrm{a}}=6.2\right)$.

Which of the following isomers has highest boiling point?