The main buffer present in our blood is.....

$pH$ of a mixture of $1 \ M$ benzoic acid $(pK_a = 4.20)$ and $1 \ M$ $C_6H_5COONa$ is $4.5$. What is the volume of benzoic acid required to prepare a $300 \ mL$ buffer solution (in $mL$)? $[\log 2 = 0.3]$

$A$ buffer solution is prepared by mixing $0.2 \ M \ NH_4OH$ and $1 \ M \ NH_4Cl$. What is the $pH$ value of the buffer solution? (Given $pK_b = 4.744$)

What volume (in $mL$) of $0.10 \, M$ sodium formate is required to be added to $50 \, mL$ of $0.05 \, M$ formic acid to prepare a buffer solution with $pH = 4.0$? (Given: $pK_a$ of formic acid $= 3.7$)

$A$ buffer solution is formed by a weak acid and its salt with a strong base,or a weak base and its salt with a strong acid. In which of the following pairs is this characteristic found?

Calculate the $pH$ of a buffer solution containing $6.1 \times 10^{-2} \ M$ sodium acetate $(CH_3COONa)$ in $1 \ L$ of $0.1 \ M$ acetic acid $(CH_3COOH)$ solution. (Given: $pK_a$ of $CH_3COOH = 4.76$)