If a certain element has an atomic number 19 , the element is

Options

A. a metal with oxidation number +1
B. an inert gas
C. a non metal with oxidation number +3
D. a metal with oxidation number +3

Explanation

To determine the element with atomic number 19, we can follow these steps:

### Step 1: Identify the Element
The atomic number of an element corresponds to the number of protons in its nucleus. For atomic number 19, the element is potassium (K).

### Step 2: Determine the Electronic Configuration
The electronic configuration of potassium can be derived as follows:
- The first shell can hold 2 electrons (1s²).
- The second shell can hold 8 electrons (2s² 2p⁶).
- The third shell can hold 8 electrons (3s² 3p⁶).
- The fourth shell starts filling with 1 electron (4s¹).

Thus, the complete electronic configuration for potassium is:
\[ \text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2 \text{3p}^6 \text{4s}^1 \]

### Step 3: Identify the Block of the Element
Since the last electron is in the s-orbital (4s¹), potassium belongs to the s-block of the periodic table.

### Step 4: Determine the Oxidation State
Alkali metals, which include potassium, typically have one electron in their outermost shell. They tend to lose this electron to achieve a stable electronic configuration, resulting in an oxidation state of +1.

### Conclusion
Given the above analysis, potassium (K) is a metal with an oxidation number of +1. Therefore, the correct answer is:
**Option A: a metal with oxidation number +1.**

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