Q. Which of the statements is not true?
A) K₂Cr₂O₇ solution becomes yellow on increasing the pH beyond 7
B) On passing H₂S through acidified K₂Cr₂O₇ solution, a milky colour is observed
C) Na₂Cr₂O₇ is preferred over K₂Cr₂O₇ in volumetric analysis
D) K₂Cr₂O₇ solution in acidic medium is orange
Explanation
[Solution from source] Na₂Cr₂O₇ is hygroscopic, so K₂Cr₂O₇, which is not, is preferred as a primary standard in volumetric analysis; the statement favouring sodium dichromate is false. The others are true: raising pH converts orange Cr₂O₇²⁻ to yellow CrO₄²⁻, and H₂S is oxidised to colloidal sulphur, giving a milky appearance. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.