What is the $pH$ of a buffer solution prepared by mixing $0.01 \ M$ weak acid and $0.02 \ M$ salt of weak acid with a strong base? $(pK_{a} = 4.680)$

Which of the following mixtures forms a buffer solution?

Find the $pH$ of a buffer solution prepared by mixing $300 \, mL$ of $0.3 \, M \, NH_3$ and $500 \, mL$ of $0.5 \, M \, NH_4Cl$. Given $K_b$ for $NH_3 = 1.8 \times 10^{-5}$.

In which of the following does a buffer solution play an important role?

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

The $K_a$ of $CH_3COOH$ is $1.8 \times 10^{-5}$. How many grams of $CH_3COONa$ are required in $0.1 \ M \ CH_3COOH$ to form a solution having $pH = 4.0$? (Molecular mass of $CH_3COONa = 82 \ g \ mol^{-1}$)