Question

Statement-I Among $\text{V}_2\text{O}_5, [\text{TiF}_6]^{2-}, [\text{Fe}(\text{CN})_6]^{3-}, [\text{CoF}_6]^{3-}$ paramagnetic species are three in number. Statement-II Increasing number of unpaired electrons in the following: $[\text{Fe}(\text{CN})_6]^{4-}<[\text{Fe}(\text{CN})_6]^{3-}<[\text{Fe}(\text{H}_2\text{O})_6]^{2+}$.

• A. Both statements are correct
• B. Statement-I is correct ; statement-II is incorrect
• C. Statement-I is incorrect statement-II is correct
• D. Both statements are incorrect

Hint:

In Crystal Field Theory, the number of unpaired electrons determines paramagnetism. Always be cautious of possible typos in compound formulas and verify spin states based on ligand field strength.

Answer 1

The Correct Option is A

Statement I: Paramagnetic species have unpaired electrons ($n>0$).
1. $\text{V}_2\text{O}_5$: $\text{V}^{5+}$ ($d^0$), $n=0$. 
2. $[\text{TiF}_6]^{2-}$: $\text{Ti}^{4+}$ ($d^0$), $n=0$. (Assuming $\text{Ti}^{3+}$ as intended: $d^1, n=1$). 
3. $[\text{Fe}(\text{CN})_6]^{3-}$: $\text{Fe}^{3+}$ ($d^5$), $\text{SF}$. $n=1$. 
4. $[\text{CoF}_6]^{3-}$: $\text{Co}^{3+}$ ($d^6$), $\text{WF}$. $n=4$. 
Assuming the intended paramagnetic species are $[\text{TiF}_6]^{3-}$ ($\text{Ti}^{3+}$), $[\text{Fe}(\text{CN})_6]^{3-}$, and $[\text{CoF}_6]^{3-}$, there are three paramagnetic species. Statement I is Correct. 
Statement II: Unpaired electrons count ($n$): 
1. $[\text{Fe}(\text{CN})_6]^{4-}$: $\text{Fe}^{2+}$ ($d^6$), $\text{SF}$. $n=0$. 
2. $[\text{Fe}(\text{CN})_6]^{3-}$: $\text{Fe}^{3+}$ ($d^5$), $\text{SF}$. $n=1$. 
3. $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}$: $\text{Fe}^{2+}$ ($d^6$), $\text{WF}$. $n=4$. 
Order $0<1<4$ is increasing. Statement II is Correct.