Which combination of the following substances will result in the formation of an acidic buffer when mixed?

1.	Weak acid and it's salt with a strong base.
2.	Equal volumes of equimolar solutions of weak acid and weak base.
3.	Strong acid and its salt with a strong base.
4.	Strong acid and its salt with a weak base. (The pKa of acid = pKb of the base)

Consider the following reaction taking place in 1L capacity container at 300 K.
\(\mathrm{A +B \rightleftharpoons C+D }\)
If one mole each of A and B are present initially and at equilibrium 0.7 mol of C is formed, then the equilibrium constant \((K_c) \) for the reaction is

The solubility product of \(\mathrm{BaSO_4}\) in water is \(1.5 \times 10^{-9} \). The molar solubility of \(\mathrm{BaSO_4}\) in 0.1 M solution of Ba(NO₃)₂ in- 
1. \(2.0 \times 10^{-8} M\)
2. \(0.5 \times 10^{-8} M\)
3. \(1.5 \times 10^{-8} M\)
4. \(1.0 \times 10^{-8} M\)

\(3 \mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{O}_{3}(\mathrm{g}) \) 
For the above reaction at 298 K, \(\text K_c\) is found to be \(3.0 \times 10^{-59} \). If the concentration of \(\text O_2\) at equilibrium is 0.040 M, then the concentration of \(\text O_3 \) in M is: 
1. \(1.2 \times 10^{21} \)
2. \(4.38 \times 10^{-32} \)
3. \(1.9 \times 10^{-63} \)
4. \(2.4 \times 10^{31} \)