Question 80: Which of the following statements are INCORRECT?
A. All the transition metals except scandium form MO oxides which are ionic.
B. The highest oxidation number corresponding to the group number in transition metal oxides is attained in \mathrm{Sc}_{2} \mathrm{O}_{3} to \mathrm{Mn}_{2} \mathrm{O}_{7}.
C. Basic character increases from \mathrm{V}_{2} \mathrm{O}_{3} to \mathrm{V}_{2} \mathrm{O}_{4} to \mathrm{V}_{2} \mathrm{O}_{5}.
D. \mathrm{V}_{2} \mathrm{O}_{4} dissolves in acids to give
\mathrm{VO}_{4}^{3-} salts.
E. CrO is basic but \mathrm{Cr}_{2} \mathrm{O}_{3} is amphoteric.
Choose the correct answer from the options given below :
(1) C and D only
(2) B and C only
(3) A and E only
(4) B and D only
Answer: Option (1)
Explanation:
Statement A is correct because most transition metals form monoxide oxides
\mathrm{MO} which are largely ionic, except scandium.
Statement B is correct because from scandium to manganese, the maximum oxidation state
shown by transition metals in their oxides increases and corresponds to their group number,
as seen from \mathrm{Sc}_{2}\mathrm{O}_{3} to
\mathrm{Mn}_{2}\mathrm{O}_{7}.
Statement C is incorrect because the basic character actually decreases with increase in oxidation state.
\mathrm{V}_{2}\mathrm{O}_{3} is basic, \mathrm{V}_{2}\mathrm{O}_{4} is
amphoteric, and \mathrm{V}_{2}\mathrm{O}_{5} is acidic.
Statement D is incorrect because \mathrm{V}_{2}\mathrm{O}_{4} dissolves in acids to form
vanadyl ions \mathrm{VO}^{2+}, not \mathrm{VO}_{4}^{3-} ions,
which are formed from \mathrm{V}_{2}\mathrm{O}_{5} in alkaline medium.
Statement E is correct because CrO is basic, while \mathrm{Cr}_{2}\mathrm{O}_{3}
shows amphoteric behaviour.
Therefore, the incorrect statements are C and D, and the correct answer is option (1).