The energy required to pull the most loosely bound electron form an atom is known as ionizatino potential it is expressed in electron volts. The value of ionization potntial depends on three factors: (i) the charge on the nucleus (ii) the atomic radius and (iii) the screening effect of inner electron shells.
Q. Which of the following elements has the least ionization potential?

Options

A. Lithium
B. Cesium
C. Magnesium
D. Calcium

Answer

To determine which element has the least ionization potential, we will analyze the factors that affect ionization potential and compare the elements given in the question. Here’s a step-by-step solution:

### Step 1: Understand Ionization Potential
Ionization potential (or ionization energy) is the energy required to remove the most loosely bound electron from an atom in its gaseous state. It is influenced by several factors, including:
- The charge on the nucleus (higher charge means higher ionization potential)
- The atomic radius (larger radius generally means lower ionization potential)
- The screening effect of inner electron shells (more inner shells mean lower ionization potential)

### Step 2: Identify the Elements
Let's assume the elements we are comparing are from the same group or period. For example, we might be comparing elements like lithium (Li), sodium (Na), potassium (K), and cesium (Cs).

### Step 3: Analyze the Group Trend
As we move down a group in the periodic table:
- The atomic radius increases due to the addition of electron shells.
- The ionization potential decreases because the outermost electrons are farther from the nucleus and are shielded by inner electrons.

### Step 4: Compare the Elements
If we compare the elements:
- Lithium (Li) has a smaller atomic radius and higher ionization potential.
- Sodium (Na) is larger than lithium, so it has a lower ionization potential than lithium.
- Potassium (K) is larger than sodium, so it has a lower ionization potential than sodium.
- Cesium (Cs) is the largest among these, hence it has the lowest ionization potential.

### Step 5: Conclusion
Based on the analysis, cesium (Cs) has the largest atomic radius and therefore the least ionization potential among the elements compared.

### Final Answer
**Cesium (Cs) has the least ionization potential.**

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