Which of the following has the highest ionization potential?

Options

A. Magnesium
B. Barium
C. Strontium
D. Calcium

Answer

To determine which of the given elements has the highest ionization potential, we need to analyze the trends in ionization potential within the group of elements provided: magnesium (Mg), barium (Ba), strontium (Sr), and calcium (Ca).

### Step-by-Step Solution:

1. **Understanding Ionization Potential**:
- Ionization potential (or ionization energy) is the energy required to remove the most loosely bound electron from an atom.
- It is also known as ionization enthalpy.

2. **Identifying the Group**:
- All the elements in the question belong to Group 2 of the periodic table, which includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

3. **Trends in the Periodic Table**:
- As we move down a group in the periodic table, the atomic size increases due to the addition of electron shells.
- Increased atomic size results in a greater distance between the nucleus and the outermost electrons.

4. **Effect of Atomic Size on Ionization Potential**:
- With an increase in atomic size, the force of attraction between the nucleus (which has a positive charge) and the outermost electrons decreases.
- Consequently, the energy required to remove an electron (ionization potential) decreases as you move down the group.

5. **Comparing the Elements**:
- **Magnesium (Mg)**: Has the smallest atomic size among the given options, with 3 electron shells.
- **Calcium (Ca)**: Has 4 electron shells, larger than magnesium.
- **Strontium (Sr)**: Has 5 electron shells, larger than calcium.
- **Barium (Ba)**: Has 6 electron shells, the largest among the options.

6. **Conclusion**:
- Since magnesium has the smallest atomic size and the highest attraction between the nucleus and its outermost electron, it will have the highest ionization potential among the given options.
- Therefore, the correct answer is **magnesium (Mg)**.

### Final Answer:
**Magnesium (Mg) has the highest ionization potential among the given options.**