Question

Consider the following two complex ions: [CoF\(_6\)]\(^{3-}\) and [Co(C\(_2\)O\(_4\))\(_3\)]\(^{3-}\). Which of the following statements is/are false?

• A. (II) and (III)
• B. (II), (III) and (IV)
• C. (III) only
• D. (III) and (IV)
• E. (I), (II) and (IV)

Hint:

Weak ligand → high spin → paramagnetic Strong ligand → low spin → diamagnetic

Answer 1

The Correct Option is A

Concept: Coordination chemistry (geometry, magnetism, oxidation state)
---

Step 1: Oxidation state of Co

• In both complexes: \[ x + (-6) = -3 \Rightarrow x = +3 \]
• So Co is +3 in both ---

Step 2: Geometry

• Both are octahedral complexes ✔ Statement (I) is TRUE ---

Step 3: Magnetic behavior

• [CoF$_6$]$^{3-}$ → weak field ligand → high spin → paramagnetic
• [Co(C$_2$O$_4$)$_3$]$^{3-}$ → stronger field → low spin → diamagnetic ✔ Statement (II) is TRUE ---

Step 4: Orbital type

• F$^-$ → outer orbital complex
• Oxalate → inner orbital complex ❌ Statement (III) is FALSE ---

Step 5: Oxidation state comparison
✔ Same in both → TRUE --- Final Answer: \[ \boxed{(III)\text{ is false}} \Rightarrow \boxed{(A)} \]