Final answer:
To create a buffer with a pH of 5.2, you should use a weak acid and its conjugate base with a pKa close to 5.2. The buffer will resist the addition of NaOH effectively if it's concentrated enough, typically at least 0.500 M.
Step-by-step explanation:
To make a buffer with a pH of 5.2 that resists the addition of 50 mmol of NaOH, you should select a weak acid and its conjugate base with a pKa close to the desired pH. The most efficient buffer capacity is when the pH is close to the pKa of the weak acid. An example of such a buffer could be made from acetic acid (HC2H3O2) and sodium acetate (NaC2H3O2), where acetic acid is the weak acid and sodium acetate is the conjugate base. When NaOH is added to this buffer system, the OH- ions react with the acetic acid to form water and the acetate ion, while the sodium ions remain spectator ions, thus the pH of the buffer changes only minimally.
Option D, which suggests the buffer is unable to resist the addition of 50 mmol of NaOH due to insufficient buffering capacity, could be relevant if the concentration of the buffer components is too low. However, typically a concentration of at least 0.500 M for buffer components is adequate to resist such changes in pH, but this requires knowing the specific concentrations and the buffer's capacity.