The titration curve for weak acid and weak base has no sharp changes. For this titration no suitable indicator is present.ReasonIndicator should change its colour sharply for indication of reaction to be complete so its PH-range lies perfectly within sharp change to avoid experimental error.A.Both assertion and reason are correct and reason is the correct explanation for assertionB.Both assertion and reason are correct but reason is not the explanation of assertionC.Assertion is correct but reason is incorrectD.Assertion is incorrect but reason is correct.

The correct answer is:
C. Assertion is correct but reason is incorrect

Explanation:
The assertion that the titration curve for a weak acid and a weak base has no sharp changes is correct. Weak acids and weak bases do not undergo complete ionization in water, and their titration curves typically show gradual changes in pH over a wide range of added titrant.

However, the reason given for why no suitable indicator is present is incorrect. The reason states that the indicator should change its color sharply within a pH range to avoid experimental error. While it's true that indicators should have a pH range that matches the region of rapid pH change in the titration curve (known as the equivalence point), this is not the primary reason why no suitable indicator is present for a titration involving weak acids and weak bases.

The main reason no suitable indicator is present is because weak acid-weak base titrations have a relatively gradual change in pH near the equivalence point. Indicators are chosen based on their pKa values, which should be close to the pH at the equivalence point to provide a clear color change. In the case of weak acid-weak base titrations, the pH range of the equivalence point is not well-defined, making it challenging to find an indicator that would give a sharp color change within that pH range.

So, while the assertion is correct, the reason provided is not the correct explanation for the absence of a suitable indicator.