The most reactive element among the following is:

Options

A. Na
B. K
C. Ca
D. Mg

Explanation

To determine the most reactive element among the given options (sodium, potassium, calcium, and magnesium), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reactivity Series**:
- The reactivity series is a list of metals arranged in order of decreasing reactivity. The higher an element is on the list, the more reactive it is.

2. **Identify the Elements in the Options**:
- The elements given in the question are sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg).

3. **Locate the Elements in the Reactivity Series**:
- According to the reactivity series:
- Potassium (K) is at the top, indicating it is very reactive.
- Sodium (Na) is below potassium but still very reactive.
- Calcium (Ca) is below sodium.
- Magnesium (Mg) is below calcium.

4. **Compare the Reactivity**:
- Since potassium is at the top of the list, it is the most reactive among the options provided.
- The order of reactivity from most to least reactive in the options is:
- Potassium > Sodium > Calcium > Magnesium.

5. **Conclusion**:
- Therefore, the most reactive element among the given options is **Potassium (K)**.

### Final Answer:
The most reactive element among the following is **Potassium (K)**.

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