Why is phenolphthalein an appropriate indicator for titration of a strong acid with a strong base?

Titrating a strong acid with a strong base results in a salt that is neutral. Phenolphthalein changes color in the range 8.3 – 10. It is very easy to spot the change as it is colorless in acidic (< 8.3) and pink in basic (> 10).

pH will rapidly change near titration equivalence point. Only one drop of the titrant causes this large change, the color change of phenolphthalein does not occur on the equivalence point, but IT IS within about 1 drop. It would be considered an "acceptable uncertainty" in using titration to determine concentration by volumetric measurement.

A.(nh4)(2co3)is the correct answer