In an acidic buffer,$0.25 \ M$ $CH_3COOH$ is added to $0.125 \ M$ $NaCH_3COO$ solution. Calculate the $pH$ of the buffer. Given $K_a$ of $CH_3COOH = 1.8 \times 10^{-5}$. [Formula: $pH = pK_a + \log \frac{[Salt]}{[Acid]}$]

$50 \, mL$ of $2 \, N$ acetic acid mixed with $10 \, mL$ of $1 \, N$ sodium acetate solution will have an approximate $pH$ of $(K_a = 10^{-5})$

Which of the following may be added to one litre of water to act as a buffer?

At $25 \, ^\circ C$,the $K_a$ for $HCN$ is $5 \times 10^{-10}$. What volume (in $mL$) of $5 \, M \, KCN$ solution must be added to $10 \, mL$ of $2 \, M \, HCN$ solution to maintain a constant $pH$ of $9$?

One litre buffer solution was prepared by adding $0.10 \ mol$ each of $NH_3$ and $NH_4Cl$ in deionised water. The change in $pH$ on addition of $0.05 \ mol$ of $HCl$ to the above solution is $............ \times 10^{-2}$ ($Nearest$ $integer$) ($Given$: $pK_b$ of $NH_3 = 4.745$ and $\log_{10} 3 = 0.477$)

Buffer Solution	Volume of $0.1 \ M$ Weak Acid (mL)	Volume of $0.1 \ M$ Sodium Salt (mL)
$I$	$4.0$	$4.0$
$II$	$4.0$	$40.0$
$III$	$40.0$	$4.0$
$IV$	$0.1$	$10.0$

Which of the two sets of buffer solutions have the least $pH$?