Ionisation energies three hypothetical elements are given below (in kJ/mole) :
`{:(,I,II,III),(X,122,340,1890),(Y,99,931,1100),(Z,118,1220,16552):}`
Which of the following is likely to be 2nd group element?

Options

A. X
B. Z
C. Y
D. X and Y

Answer

To determine which of the hypothetical elements (X, Y, or Z) is likely to be a second group element (alkaline earth metal), we will analyze the given ionization energies (IE) for each element. The general electronic configuration for alkaline earth metals is ns², which means that the first two ionization energies should not be significantly different, but there should be a large jump between the second and third ionization energies.

### Step-by-step Solution:

1. **List the Ionization Energies:**
- For Element X: IE1 = 122 kJ/mol, IE2 = 340 kJ/mol, IE3 = 1890 kJ/mol
- For Element Y: IE1 = 99 kJ/mol, IE2 = 931 kJ/mol, IE3 = 1100 kJ/mol
- For Element Z: IE1 = 118 kJ/mol, IE2 = 1220 kJ/mol, IE3 = 16552 kJ/mol

2. **Analyze the Differences Between Ionization Energies:**
- For Element X:
- Difference between IE1 and IE2: 340 - 122 = 218 kJ/mol
- Difference between IE2 and IE3: 1890 - 340 = 1550 kJ/mol
- For Element Y:
- Difference between IE1 and IE2: 931 - 99 = 832 kJ/mol
- Difference between IE2 and IE3: 1100 - 931 = 169 kJ/mol
- For Element Z:
- Difference between IE1 and IE2: 1220 - 118 = 1102 kJ/mol
- Difference between IE2 and IE3: 16552 - 1220 = 15332 kJ/mol

3. **Identify the Element with a Large Jump in Ionization Energies:**
- Element X shows a significant jump from IE2 to IE3 (1550 kJ/mol), indicating that after removing the second electron, the next electron is being removed from a much more stable electron configuration (noble gas configuration).
- Element Y does not show a large jump between IE2 and IE3.
- Element Z has an extremely large jump from IE2 to IE3 (15332 kJ/mol), but the difference between IE1 and IE2 is also significant, which is not typical for alkaline earth metals.

4. **Conclusion:**
- Based on the analysis, Element X is the most likely candidate to be a second group element (alkaline earth metal) because it has a reasonable difference between IE1 and IE2, and a large jump between IE2 and IE3.

### Final Answer:
The element likely to be a second group element is **Element X**.