A change of Zn to `Zn^(2+)` is a accompanied by a decrease in:

Options

A. Number of valence electrons
B. atomic mass
C. number of shells
D. none of these

Answer

To solve the question regarding the change of Zn to Zn²⁺ and what decreases as a result, we can follow these steps:

### Step 1: Determine the electronic configuration of Zn
- The atomic number of Zinc (Zn) is 30. Therefore, its electronic configuration is:
\[ \text{Zn: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} \]

### Step 2: Determine the electronic configuration of Zn²⁺
- When Zinc loses two electrons to form Zn²⁺, the electrons are removed from the outermost shell (4s orbital) first. Thus, the electronic configuration of Zn²⁺ becomes:
\[ \text{Zn}^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} \]

### Step 3: Analyze the changes in the number of valence electrons
- In the neutral Zn atom, the valence electrons are those in the outermost shell (4s and 3d). For Zn, the valence electrons are:
- 4s² (2 electrons) + 3d¹⁰ (10 electrons) = 12 valence electrons.
- In Zn²⁺, the valence electrons are:
- 3d¹⁰ (10 electrons) = 10 valence electrons.
- Therefore, the number of valence electrons decreases from 12 to 10.

### Step 4: Analyze the changes in atomic mass
- The atomic mass of an element is determined by the number of protons and neutrons in the nucleus. The loss of electrons does not affect the atomic mass, so it remains the same.

### Step 5: Analyze the changes in the number of shells
- The principal quantum number (n) indicates the number of shells. For Zn, the highest principal quantum number is 4 (from the 4s orbital), indicating 4 shells.
- For Zn²⁺, the highest principal quantum number is 3 (from the 3d orbital), indicating 3 shells.
- Therefore, the number of shells decreases from 4 to 3.

### Conclusion
- The change of Zn to Zn²⁺ is accompanied by a decrease in the number of shells.

### Final Answer
The correct option is: **Number of shells decreases.**

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