$A$ buffer solution of $100 \ mL$ has a $pH$ value of $4$. When $1 \ mL$ of dilute $HCl$ is added to it,what happens to the $pH$ of the buffer solution?

Which of the following mixtures will have the lowest $pH$ at $298 \ K$?

Which of the following solutions does not act as a buffer $:-$

The buffer system which helps to maintain the $pH$ of blood between $7.26$ to $7.42$ is:

If $20 \ mL$ of $0.1 \ M \ NaOH$ is added to $30 \ mL$ of $0.2 \ M \ CH_3COOH$ $(pK_a = 4.74)$,the $pH$ of the resulting solution is

Assertion $(A)$: The $pH$ of a buffer solution containing equal moles of acetic acid and sodium acetate is $4.8$ ($pK_a$ of acetic acid is $4.8$).
Reason $(R)$: The ionic product of water at $25^{\circ} C$ is $10^{-14} \ mol^2 \ L^{-2}$. The correct answer is