Question

Lanthanoid ions with \(4f^7\) configuration are: (A) Eu\(^{2+}\) (B) Gd\(^{3+}\) (C) Eu\(^{3+}\) (D) Tb\(^{3+}\) (E) Sm\(^{2+}\) Choose the correct answer from the options given below:

• (A) and (B) only
• (A) and (D) only
• (B) and (E) only
• (B) and (C) only

Hint:

Remember the electronic configurations of lanthanoid ions and how to determine the number of 4f electrons.

Answer 1

The Correct Option is A

Step 1: Write the electronic configurations.

\(_{63}\)Eu\(^{2+}\) - [Xe] 4f\(^7\) 6s\(^0\)
\(_{64}\)Gd\(^{3+}\) - [Xe] 4f\(^7\) 5d\(^0\) 6s\(^0\)
\(_{63}\)Eu\(^{3+}\) - [Xe] 4f\(^6\) 6s\(^0\)
\(_{65}\)Tb\(^{3+}\) - [Xe] 4f\(^8\) 6s\(^0\)
\(_{62}\)Sm\(^{2+}\) - [Xe] 4f\(^6\) 6s\(^0\)

Step 2: Identify the ions with 4f\(^7\) configuration.

From the electronic configurations, we can see that Eu\(^{2+}\) and Gd\(^{3+}\) have 4f\(^7\) configurations.

Step 3: Select the correct option.

Therefore, the correct answer is (A) and (B) only.

Answer 2

Step 1 — Recall the general electronic configuration of lanthanoids:

The general configuration of lanthanoids is: \[ [\text{Xe}]\,4f^{1-14}\,5d^{0-1}\,6s^2 \]

Step 2 — Determine the \(4f\) configuration for each ion:

• (A) Eu\(^{2+}\)
  Neutral Eu: [Xe] 4f⁷ 6s²
  After losing 2 electrons → Eu\(^{2+}\): [Xe] 4f⁷
  ✅ Has \(4f^7\) configuration.
• (B) Gd\(^{3+}\)
  Neutral Gd: [Xe] 4f⁷ 5d¹ 6s²
  After losing 3 electrons → Gd\(^{3+}\): [Xe] 4f⁷
  ✅ Has \(4f^7\) configuration.
• (C) Eu\(^{3+}\)
  Eu\(^{3+}\): [Xe] 4f⁶ ❌ (not 4f⁷)
• (D) Tb\(^{3+}\)
  Tb\(^{3+}\): [Xe] 4f⁸ ❌ (not 4f⁷)
• (E) Sm\(^{2+}\)
  Sm\(^{2+}\): [Xe] 4f⁶ ❌ (not 4f⁷)

Step 3 — Correct pair:

The ions with \(4f^7\) configuration are Eu\(^{2+}\) and Gd\(^{3+}\).

Final Answer:

✅ (A) and (B) only