Question

Which of the following is/are correct?
i. Cr$_2$O$_3$ is an acidic oxide
ii. Mo(VI) and W(VI) are more stable than Cr(VI)
iii. All Cu(II) halides are known except iodide
iv. The E$^\circ$ value for Cr$^{3+}$/Cr$^{2+}$ is much more positive than Mn$^{3+}$/Mn$^{2+}$

• A. i, ii, iii only
• B. iv only
• C. ii, iv only
• D. i, iii only

Hint:

Know the stability of oxidation states and solubility of halides to eliminate incorrect options.

Answer 1

The Correct Option is A

- i. Cr$_2$O$_3$ is amphoteric, not acidic ⇒ incorrect
- ii. Mo and W in +6 oxidation state are more stable than Cr(VI) ⇒ correct
- iii. CuI is unstable due to disproportionation, others exist ⇒ correct
- iv. E$^\circ$ for Cr$^{3+}$/Cr$^{2+}$ is less positive than Mn$^{3+}$/Mn$^{2+}$ ⇒ incorrect