Answer :
In chemistry, buffers are solutions that resist changes in pH when small amounts of an acid or a base are added. A buffer contains a weak acid and its conjugate base or a weak base and its conjugate acid.
For a weak acid to act effectively as a buffer, the pH of the solution should be close to the pKa value of that acid. This is because the effectiveness of the buffer is strongest when the concentrations of the acid and its conjugate base are approximately equal, which typically occurs around the pKa value of the acid.
The buffering range is usually considered to be within one pH unit above or below the pKa of the acid. This is because, within this range, the ratio of the concentrations of the acid and its conjugate base allows the buffer to neutralize added acids and bases effectively.
Therefore, the correct choice for the range from a weak acid's pKa value where it can still act as a buffer is plus or minus 1.0. However, since the closest option given is plus or minus 1.5, the best answer would be:
(C) plus or minus 1.5.
