$A$ solution of $0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ and $0.08 \ mol$ of $HCl$ is diluted to $1 \ L$. The $pOH$ of the resulting solution is $(\log 1.25 = 0.1)$.

$A$ buffer solution is prepared by mixing $0.01 \ M$ weak acid and $0.05 \ M$ solution of a salt of weak acid and strong base. What is the $pH$ of the buffer solution? $(pK_a = 4.74)$

Find the $pH$ when $0.2 \, mol$ of $HCl$ is added to $1 \, L$ of a solution containing $1 \, M$ $CH_3COOH$ and $1 \, M$ $CH_3COO^-$. Assume the total volume remains $1 \, L$. Given $K_a$ for $CH_3COOH = 1.8 \times 10^{-5}$.

To prepare a buffer solution of $pH = 6$ by mixing sodium acetate and acetic acid,what should be the ratio of the concentration of salt to acid? $(K_a = 10^{-5})$

Which statement is correct for a mixture of $1 \ M \ NaCl$ and $1 \ M \ HCl$?

Study the following table:

Buffer Solution	Volume (in $mL$) of $0.1 \ M$ Weak acid	Volume (in $mL$) of $0.1 \ M$ sodium salt of weak acid
$I$	$4.0$	$4.0$
$II$	$4.0$	$40.0$
$III$	$40.0$	$4.0$
$IV$	$0.1$	$10.0$

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