Which of the following solutions can act as a buffer?

$A$ solution contains $0.1 \ mol$ of acetic acid and $0.1 \ mol$ of sodium acetate in $500 \ mL$ of solution. If the $pH$ of the solution is $4.74$,find the ionization constant $(K_a)$ of acetic acid.

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? $(K_a = 10^{-5})$

Assertion : In a titration of weak acid and $NaOH$,the $pH$ at half equivalence point is $pK_a$.
Reason : At half equivalence point,it forms an acidic buffer and the buffer capacity is maximum where $[acid] = [salt]$.

$A$ buffer solution is prepared by mixing $10 \ mL$ of $1.0 \ M$ acetic acid and $20 \ mL$ of $0.5 \ M$ sodium acetate and then diluted to $100 \ mL$ with distilled water. The $pH$ of the buffer solution is ($pK_a$ of acetic acid is $4.76$).

Which of the following statements is incorrect for a buffer solution?