Which among the following elements has lowest value of ionisation potential ?

Options

A. Mg
B. Ca
C. Ba
D. Sr.

Answer

To determine which among the given elements has the lowest value of ionization potential, we can follow these steps:

### Step 1: Understand Ionization Potential
Ionization potential (or ionization energy) is defined as the energy required to remove an electron from the outermost shell of a gaseous atom.

**Hint:** Remember that ionization potential is influenced by the atomic structure and the position of the element in the periodic table.

### Step 2: Identify the Elements
The elements provided in the question are:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)

**Hint:** Make sure to recognize that all these elements belong to the alkaline earth metals group.

### Step 3: Determine the Position in the Periodic Table
These elements are arranged in the periodic table as follows:
- Beryllium (Be) is in period 2
- Magnesium (Mg) is in period 3
- Calcium (Ca) is in period 4
- Strontium (Sr) is in period 5

**Hint:** The position of an element in the periodic table can give you insight into its ionization energy.

### Step 4: Analyze the Trend in Ionization Energy
As we move down a group in the periodic table, the ionization energy generally decreases. This is because:
- The outermost electrons are further from the nucleus.
- There is increased electron shielding from the inner electrons, making it easier to remove the outermost electron.

**Hint:** Remember that the trend is from top to bottom in a group; ionization energy decreases as you go down.

### Step 5: Compare the Ionization Energies
Based on the trend:
- Beryllium (Be) has the highest ionization energy among the four.
- Magnesium (Mg) has a lower ionization energy than Beryllium.
- Calcium (Ca) has a lower ionization energy than Magnesium.
- Strontium (Sr) has the lowest ionization energy among these four elements.

**Hint:** Compare the elements based on their periods to determine which has the lowest ionization potential.

### Conclusion
Therefore, among the elements given, **Strontium (Sr)** has the lowest value of ionization potential.

**Final Answer:** Strontium (Sr) has the lowest ionization potential.