An element A has atomic mass 39 and atomic number 19. Which one of the following ions it will form on ionising one electron?

Options

A. `A^(+)` ion
B. `A^(-) `ion
C. `A^( + +)` ion
D. `A^(- -)` ion

Explanation

To determine which ion element A will form upon ionizing one electron, we can follow these steps:

### Step 1: Identify the Element
The atomic number of element A is 19. This means it has 19 protons in its nucleus. The element with atomic number 19 is Potassium (K).

### Step 2: Write the Atomic Mass
The atomic mass of element A is given as 39. This is consistent with Potassium, which has an atomic mass of approximately 39.

### Step 3: Determine the Electronic Configuration
The electronic configuration of Potassium (K) can be determined based on its atomic number (19). The distribution of electrons in the shells is as follows:
- 1st shell: 2 electrons
- 2nd shell: 8 electrons
- 3rd shell: 8 electrons
- 4th shell: 1 electron

Thus, the electronic configuration of Potassium is:
\[ \text{K: } 2, 8, 8, 1 \]

### Step 4: Identify Valence Electrons
From the electronic configuration, we can see that Potassium has 1 valence electron in its outermost shell (4th shell).

### Step 5: Determine the Ion Formed
When Potassium ionizes by losing one electron, it will lose its single valence electron to achieve a stable electronic configuration similar to that of the nearest noble gas (Argon).

After losing one electron, the electronic configuration will be:
\[ \text{K}^+: 2, 8, 8 \]

### Step 6: Identify the Charge of the Ion
Since Potassium loses one electron, it will have a positive charge. Therefore, the ion formed will be:
\[ \text{K}^+ \]

### Conclusion
The ion that element A (Potassium) will form upon ionizing one electron is \( \text{K}^+ \).

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