Question

Read the following statements: I. Trivalent chromium has relatively low aqueous solubility, and low mobility in the soil environment. By contrast, hexavalent chromium has a higher aqueous solubility and greater mobility in the soil environment.
II. The chemical reaction between trivalent chromium and zero-valent iron will result in transformed version called hexavalent chromium.
III. Hexavalent chromium is a known carcinogen.
IV. Trivalent chromium has relatively higher human toxicity as compared to hexavalent chromium.
The correct choice is:

• A. IV is correct; I and III are incorrect
• B. II is correct; I and IV are incorrect
• C. I and III are correct; II and IV are incorrect
• D. I, II and IV are correct; III is incorrect

Hint:

- Cr(III): stable, less toxic, essential in trace amounts.
- Cr(VI): soluble, mobile, carcinogenic, highly toxic.
- Zero-valent iron reduces Cr(VI) → Cr(III).

Answer 1

The Correct Option is C

Step 1: Statement I.
- Cr(III) = low solubility, low mobility. - Cr(VI) = high solubility, highly mobile. Hence, Statement I is correct.
Step 2: Statement II.
- Reaction with zero-valent iron reduces hexavalent chromium (Cr VI) → trivalent chromium (Cr III). - It does not produce Cr(VI). Hence, Statement II is incorrect.
Step 3: Statement III.
- Cr(VI) is highly toxic and a known carcinogen. Hence, Statement III is correct.
Step 4: Statement IV.
- Cr(III) is an essential trace element, less toxic. - Cr(VI) is far more toxic. Hence, Statement IV is incorrect.
Step 5: Conclusion.
Correct statements = I and III → Option (C). Final Answer: \[ \boxed{\text{(C) I and III are correct; II and IV are incorrect}} \]