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JEE MAIN Chemistry QUESTION #1010
Question 1
Identify the homoleptic complex(es) that is/are low spin. (A) \([\text{Fe(CN)}_5\text{NO}]^{2-}\) (B) \([\text{CoF}_6]^{3-}\) (C) \([\text{Fe(CN)}_6]^{4-}\) (D) \([\text{Co(NH}_3)_6]^{3+}\) (E) \([\text{Cr(H}_2\text{O)}_6]^{2+}\)
  • (C) only
  • (C) and (D) only✔️
  • (A) and (C) only
  • (B) and (E) only
Correct Answer Explanation
Homoleptic = only one type of ligand. (A) has \(\text{CN}^-\) and NO — not homoleptic. (B) \([\text{CoF}_6]^{3-}\): F is weak field → high spin. (C) \([\text{Fe(CN)}_6]^{4-}\): \(\text{CN}^-\) is strong field → low spin, homoleptic. (D) \([\text{Co(NH}_3)_6]^{3+}\): \(\text{NH}_3\) is moderate-strong field on \(\text{Co}^{3+}\) → low spin, homoleptic. So (C) and (D) are both homoleptic and low spin.