Which of the following mixtures in water acts as a buffer?

Under which condition does a basic buffer follow the equation $pOH - pK_b = 1$?

$20 \ mL$ of $0.1 \ (N)$ acetic acid is mixed with $10 \ mL$ of $0.1 \ (N)$ solution of $NaOH$. The $pH$ of the resulting solution is ($pK_a$ of acetic acid is $4.74$). (in $.74$)

Calculate the $pH$ of a $0.10 \,M$ ammonia solution. Calculate the $pH$ after $50.0 \,mL$ of this solution is treated with $25.0 \,mL$ of $0.10 \,M$ $HCl$. The dissociation constant of ammonia,$K_{b} = 1.77 \times 10^{-5}$.

$2 \ g$ acetic acid and $3 \ g$ sodium acetate are present in $100 \ mL$ aqueous solution. What will be the $pH$ of the solution if the ionisation constant of acetic acid is $1.8 \times 10^{-5}$?

Which of the following will form a basic buffer solution?