The number of electron and proton in the third alkaline earth metal ion will be

Options

A. `e/20,p/20`
B. `e/18,p/20`
C. `e/18,p/18`
D. `e/19,p/20`

Explanation

To solve the question regarding the number of electrons and protons in the third alkaline earth metal ion, we will follow these steps:

### Step 1: Identify the third alkaline earth metal
The alkaline earth metals are located in Group 2 of the periodic table. The first three alkaline earth metals are:
1. Beryllium (Be) - Atomic number 4
2. Magnesium (Mg) - Atomic number 12
3. Calcium (Ca) - Atomic number 20

Thus, the third alkaline earth metal is Calcium (Ca).

### Step 2: Determine the number of protons
The atomic number of Calcium (Ca) is 20. The atomic number of an element is equal to the number of protons in its nucleus. Therefore, Calcium has:
- **Number of protons = 20**

### Step 3: Determine the ion form of Calcium
Calcium typically forms a +2 ion (Ca²⁺) when it loses two electrons to achieve a stable electron configuration.

### Step 4: Calculate the number of electrons in the Ca²⁺ ion
In its neutral state, Calcium has 20 electrons (equal to the number of protons). When it forms the Ca²⁺ ion, it loses 2 electrons:
- **Number of electrons in Ca²⁺ = 20 (neutral) - 2 (lost) = 18**

### Step 5: Summarize the results
- **Number of protons in Ca²⁺ = 20**
- **Number of electrons in Ca²⁺ = 18**

### Final Answer:
The number of electrons in the third alkaline earth metal ion (Ca²⁺) is 18, and the number of protons is 20.

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