An element X has atomic number 19.What will be the formula of its oxide?

Options

A. `X_(2)O`
B. XO
C. `XO_(2)`
D. `X_(2)O_(3)`

Explanation

To determine the formula of the oxide of the element X with atomic number 19, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Element**:
- The atomic number 19 corresponds to the element Potassium (K).

2. **Determine the Electron Configuration**:
- The electron configuration of Potassium (K) is 2, 8, 8, 1. This indicates that Potassium has one electron in its outermost shell.

3. **Determine the Valency of Potassium**:
- Since Potassium has one electron in its outer shell, it tends to lose this electron to achieve a stable electronic configuration. Therefore, the valency of Potassium is +1.

4. **Determine the Valency of Oxygen**:
- Oxygen typically has six electrons in its outer shell and needs two more electrons to complete its octet. Thus, the valency of oxygen is -2.

5. **Criss-Cross Method**:
- To find the formula of the oxide, we can use the criss-cross method. We take the valency of Potassium (+1) and the valency of Oxygen (-2).
- Criss-crossing the valencies gives us K2O (the +1 from K becomes the subscript for O, and the -2 from O becomes the subscript for K).

6. **Final Formula**:
- Therefore, the formula of the oxide of the element X (Potassium) is K2O.

### Conclusion:
The formula of the oxide of the element X with atomic number 19 is **K2O**.

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