Q.Which of the following statements is not true?

Step 1. Check each statement against the chapter's chromate/dichromate chemistry. (a) Passing H₂S through acidified K₂Cr₂O₇ gives Cr₂O₇²⁻ + 3S²⁻ + 14H⁺ → 2Cr³⁺ + 3S + 7H₂O, and the elemental sulphur produced is indeed observed as a milky turbidity -- TRUE.

Step 2. (c) In acidic solution, dichromate ion (the orange/orange-red species) is predominant, so a K₂Cr₂O₇ solution in acidic medium is genuinely orange -- TRUE. (d) Raising the pH beyond 7 (into alkaline conditions) shifts the chromate/dichromate equilibrium toward the yellow chromate ion, so the solution does turn yellow -- TRUE. …

Evaluate each statement individually against the established chemistry of chromate/dichromate interconversion and standard laboratory practice, …

• Assuming sodium dichromate (used industrially in place of K₂Cr₂O₇ where toxic-fume release is a concern, per section 4.4.2.2) is therefore also preferred analytically -- industrial substitution and analytical/primary-standard preference are two different contexts. …