Question

Identify correct statements from below:
A. The chromate ion is square planar. 
B. Dichromates are generally prepared from chromates. 
C. The green manganate ion is diamagnetic. 
D. Dark green coloured \(K_2​MnO_4\)​ disproportionates in a neutral or acidic medium to give permanganate. 
E. With increasing oxidation number of transition metal, ionic character of the oxides decreases. 
Choose the correct answer from the options given below:

• A. B, C, D only
• B. A, D, E only
• C. A, B, C only
• D. B, D, E only

Answer 1

The Correct Option is D

To determine the correct statements, let's evaluate each given option based on chemistry principles:

1. Statement A: The chromate ion is square planar.  
   Chromate ion, \( \text{CrO}_4^{2-} \), does not have a square planar geometry. It actually has a tetrahedral geometry. The chromium atom is surrounded by four oxygen atoms forming a tetrahedral shape. Therefore, this statement is incorrect.
2. Statement B: Dichromates are generally prepared from chromates. 
   Dichromates (e.g., \( \text{Cr}_2\text{O}_7^{2-} \)) are commonly prepared from chromates by acidifying the solution of chromate ions \( \text{CrO}_4^{2-} \). The reaction is as follows: 
   \(2\text{CrO}_4^{2-} + 2\text{H}^+ \rightarrow \text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{O}\) 
   This statement is correct.
3. Statement C: The green manganate ion is diamagnetic. 
   Manganate ion \( \text{MnO}_4^{2-} \) is green but it is not diamagnetic; rather, it is paramagnetic due to unpaired electrons in manganese. Thus, this statement is incorrect.
4. Statement D: Dark green coloured \( K_2\text{MnO}_4 \) disproportionates in a neutral or acidic medium to give permanganate. 
   In a neutral or acidic medium, the manganate ion undergoes disproportionation to form permanganate and manganese dioxide. The reaction is: 
   \(3\text{K}_2\text{MnO}_4 \rightarrow 2\text{KMnO}_4 + \text{MnO}_2 + 2\text{KOH}\) 
   This statement is correct.
5. Statement E: With increasing oxidation number of transition metal, ionic character of the oxides decreases. 
   As the oxidation number of a transition metal increases, the covalent character also tends to increase, because the smaller and more highly charged cations polarize the electron cloud more effectively, leading to more covalent character. This statement is correct.

From the analysis above, the correct statements are B, D, and E. Therefore, the correct answer is B, D, E only.

Answer 2

A. \( \text{CrO}_4^{2-} \) is tetrahedral.

B. \( 2\text{Na}_2\text{CrO}_4 + 2\text{H}^+ \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 + 2\text{Na}^+ + \text{H}_2\text{O} \)

C. As per NCERT, green manganate is paramagnetic with 1 unpaired electron.

D. Statement is correct.

E. Statement is correct.