Statement I: K₂Cr₂O₇ can be used as a primary standard.

Statement II: Structurally, phenolphthalein is a weak base indicator.

Choose the correct option.

• (1) Both Statement I and Statement II are correct.
• (2) Both Statement I and Statement II are incorrect.
• (3) Statement I is correct but Statement II is incorrect.
• (4) Statement I is incorrect but Statement II is correct.

Let us analyze each statement separately.

A primary standard is a highly pure, stable, non-hygroscopic substance whose solution concentration can be accurately prepared by direct weighing.

Potassium dichromate (K₂Cr₂O₇) possesses the characteristics of a primary standard:

• High purity
• Stable in air
• Non-hygroscopic nature
• High molar mass
• Can be accurately weighed

Therefore, Statement I is correct.

Now consider Statement II.

Phenolphthalein is an acid-base indicator commonly used in titrations. Structurally, it behaves as a weak acid rather than a weak base.

In acidic medium, phenolphthalein remains colorless, while in basic medium it ionizes and develops a pink color. Its indicator action is based on the equilibrium between protonated and deprotonated forms.

Since phenolphthalein is a weak acid indicator, describing it as a weak base indicator is incorrect.

Thus:

• Statement I = Correct
• Statement II = Incorrect

Questions of this type are frequently asked in competitive examinations to test conceptual understanding of volumetric analysis and acid-base indicators.

Correct Option: (3)