A buffer solution is prepared by mixing $0.2 \mathrm{~M} \mathrm{~NH} \mathrm{O}_4 \mathrm{OH}$ and $1 \mathrm{~M} \mathrm{~NH}_4 \mathrm{Cl}$. What is the pH value of buffer solution? $\left(\right.$ Give $\left.\mathrm{pK}_{\mathrm{b}}=7.744\right)$

A solution of nonvolatile solute is obtained by dissolving 0.8 g in $0.3 \mathrm{dm}^3$ water has osmotic pressure 0.2 atm at 300 K . Calculate the molar mass of solute.

$$\left[\mathrm{R}=0.082 \mathrm{~atm} \mathrm{dm}^3 \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right]$$

Which of the following molecules is an example of sp hybridization?

A first order reaction takes 40 minute for $20 \%$ decomposition. Calculate its rate constant.