Which of the following is the correct order of ionisation enthalpy ?

Options

A. `Te^(2-) lt I lt Cs lt Ba^(2+)`
B. `I^(-) lt Te^(2-) lt Cs lt Ba^(2+)`
C. `Ts^(2-) lt Cs lt I^(-) lt Ba^(2+)`
D. `Ba^(2+) lt Cs^(+) lt I^(-) lt Te^(2-)`

Explanation

To determine the correct order of ionization enthalpy for the given species (Te²⁻, I⁻, Cs⁺, and Ba²⁺), we will follow these steps:

### Step 1: Identify the Species and Their Charges
The species given are:
- Te²⁻ (Telluride ion with a -2 charge)
- I⁻ (Iodide ion with a -1 charge)
- Cs⁺ (Cesium ion with a +1 charge)
- Ba²⁺ (Barium ion with a +2 charge)

### Step 2: Determine Isoelectronic Nature
All the species mentioned are isoelectronic, meaning they have the same number of electrons. In this case, they all have the electron configuration of the noble gas Xenon (Xe).

### Step 3: Understand the Relationship Between Charge and Ionization Enthalpy
Ionization enthalpy is the energy required to remove an electron from an atom or ion. The key points to remember are:
- Ionization enthalpy increases with an increase in positive charge because a higher positive charge means a stronger attraction between the nucleus and the electrons.
- Ionization enthalpy decreases with an increase in negative charge due to increased electron-electron repulsion.

### Step 4: Compare the Charges
Now, let's analyze the charges:
- Te²⁻ has a -2 charge (lowest ionization enthalpy due to high electron-electron repulsion).
- I⁻ has a -1 charge (higher ionization enthalpy than Te²⁻).
- Cs⁺ has a +1 charge (higher ionization enthalpy than I⁻).
- Ba²⁺ has a +2 charge (highest ionization enthalpy due to the strongest attraction).

### Step 5: Establish the Order of Ionization Enthalpy
Based on the analysis of the charges:
- The order of ionization enthalpy from lowest to highest is:
1. Te²⁻ (lowest)
2. I⁻
3. Cs⁺
4. Ba²⁺ (highest)

Thus, the correct order of ionization enthalpy is:
**Te²⁻ < I⁻ < Cs⁺ < Ba²⁺**

### Final Answer
The correct answer for the order of ionization enthalpy is option A: Te²⁻ < I⁻ < Cs⁺ < Ba²⁺.

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