Question

Identify the pair of elements in which the number of electrons in the (n-1) shell is the same:

• A. Fe, Mn
• B. Zn, Fe
• C. K, Sc
• D. Mn, Cr

Hint:

Transition elements have their valence electrons in the \( (n) \) shell, while their \( (n-1) \) shell contains the d-electrons. When comparing elements, focus on the d-orbital occupancy to determine similarities in the \( (n-1) \) shell.

Answer 1

The Correct Option is D

To determine which pair of elements has the same number of electrons in the (n-1) shell, we need to analyze the electron configurations of the elements:

• Iron (Fe): [Ar] 3d⁶ 4s²
• Manganese (Mn): [Ar] 3d⁵ 4s² 
• Zinc (Zn): [Ar] 3d¹⁰ 4s²
• Potassium (K): [Ar] 4s¹
• Scandium (Sc): [Ar] 3d¹ 4s²
• Chromium (Cr): [Ar] 3d⁵ 4s¹

The (n-1) shell for the elements given is the 3rd shell, which corresponds to the 3d subshell. Let's analyze these configurations to find pairs with the same number of electrons in this shell:

• Fe (Iron): 3d⁶
• Mn (Manganese): 3d⁵
• Zn (Zinc): 3d¹⁰
• K (Potassium): 3d⁰
• Sc (Scandium): 3d¹
• Cr (Chromium): 3d⁵

We find that both Manganese (Mn) and Chromium (Cr) have 5 electrons in the 3d subshell.

Thus, the correct pair with the same number of electrons in the (n-1) shell is Mn, Cr.

Answer 2

In this problem, we need to identify the pair of elements that have the same number of electrons in the (n-1) shell, where n represents the principal quantum number.

We need to check the electron configurations of each pair of elements and compare the number of electrons in the (n-1) shell:

1. Fe and Mn:

Electron configuration of Fe: [Ar] 3d⁶ 4s²

Electron configuration of Mn: [Ar] 3d⁵ 4s²

The number of electrons in the (n-1) shell is different for both elements, so this is not the correct answer.

2. Zn and Fe:

Electron configuration of Zn: [Ar] 3d¹⁰ 4s²

Electron configuration of Fe: [Ar] 3d⁶ 4s²

The number of electrons in the (n-1) shell is different for both elements, so this is not the correct answer.

3. K and Sc:

Electron configuration of K: [Ne] 3s² 3p⁶ 4s¹

Electron configuration of Sc: [Ar] 3d¹ 4s²

The number of electrons in the (n-1) shell is different for both elements, so this is not the correct answer.

4. Mn and Cr:

Electron configuration of Mn: [Ar] 3d⁵ 4s²

Electron configuration of Cr: [Ar] 3d⁵ 4s¹

Both elements have the same number of electrons (5 electrons) in the (n-1) shell, so this is the correct answer.