The ionisation energy for 'Sc', 'Y' and 'La' are x,y and z kcal/mol respectively. Choose the correct relationship between them.

Options

A. `z gt x ~~y`
B. `x gt y gt z`
C. `z gt z ~~y`
D. `z lt y gt z`

Answer

To determine the relationship between the ionization energies of scandium (Sc), yttrium (Y), and lanthanum (La), we will analyze the trends in ionization energy across the periodic table.

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. It generally increases across a period (from left to right) and decreases down a group (from top to bottom).

2. **Position of Elements**:
- Scandium (Sc) is located in the 3rd period and is the first element of the d-block transition metals.
- Yttrium (Y) is in the 4th period and is also a d-block transition metal.
- Lanthanum (La) is in the 5th period and is the first element of the f-block.

3. **Trend in Ionization Energy**:
As we move down a group in the periodic table, the ionization energy decreases. This is due to the increase in atomic size and the shielding effect caused by the inner electron shells.

4. **Comparing Sc, Y, and La**:
- Since Sc is at the top of the group, it will have the highest ionization energy.
- Yttrium, being below Sc, will have a lower ionization energy than Sc.
- Lanthanum, being below Y, will have an even lower ionization energy than Y.

5. **Conclusion**:
Based on the above analysis, we can conclude that the ionization energies follow the relationship:
\[ X > Y > Z \]
where \(X\) is the ionization energy of Sc, \(Y\) is the ionization energy of Y, and \(Z\) is the ionization energy of La.

### Final Answer:
The correct relationship between the ionization energies is:
\[ X > Y > Z \]