To determine which of the given elements is the most reactive, let's analyze their positions in the periodic table and understand how reactivity trends down the groups (columns) of the periodic table.
### Group Trends
1. Reactivity in Group 1 (Alkali Metals):
- Group 1 elements (alkali metals) increase in reactivity as you move down the group. This is because the outer electron becomes easier to lose as the atomic radius increases, and the electron is further from the nucleus.
- Given elements in Group 1: Sodium (Na) and Potassium (K).
2. Reactivity in Group 2 (Alkaline Earth Metals):
- Group 2 elements (alkaline earth metals) also increase in reactivity as you move down the group. However, Group 1 elements are generally more reactive than Group 2 elements.
- Given elements in Group 2: Magnesium (Mg) and Calcium (Ca).
### Specific Analysis
1. Sodium (Na):
- Group 1, Period 3. It is less reactive than potassium because it is higher in the group.
2. Potassium (K):
- Group 1, Period 4. It is more reactive than sodium because it is lower in the group.
3. Magnesium (Mg):
- Group 2, Period 3. It is less reactive compared to calcium within Group 2, but less reactive than Group 1 elements.
4. Calcium (Ca):
- Group 2, Period 4. It is more reactive than magnesium but still less reactive than Group 1 elements of the same period.
### Conclusion
- By comparing the positions and the trends of reactivity:
- Potassium (K) is lower in Group 1, making it more reactive than sodium (Na).
- Calcium (Ca) is lower in Group 2 and more reactive than magnesium (Mg), but still less reactive than the Group 1 elements.
From this above analysis, Potassium (K) will be the most reactive element among Calcium (Ca), Magnesium (Mg), Potassium (K), and Sodium (Na).
Hence, the answer is: Potassium (K).
