First three ionisation energies (in kJ/mol) of three representative elements are given below:
`{:("Element",IE_(1),IE_(2),IE_(3)),(P,495.8,4582,6910),(Q,737.7,1451,7733),(R,577.5,1817.2745):}`
then incorrect option is:

Options

A. Q: alkaline earth metal
B. P: alkali metals
C. R: s-block element
D. They belong to same period

Explanation

To determine the incorrect option regarding the ionization energies of the elements P, Q, and R, we will analyze the given ionization energy values step by step.

### Step 1: Analyze the Ionization Energies
We have the following ionization energies for the elements:

- **Element P**:
- IE₁ = 495.8 kJ/mol
- IE₂ = 4582 kJ/mol
- IE₃ = 6910 kJ/mol

- **Element Q**:
- IE₁ = 737.7 kJ/mol
- IE₂ = 1451 kJ/mol
- IE₃ = 7733 kJ/mol

- **Element R**:
- IE₁ = 577.5 kJ/mol
- IE₂ = 1817.2 kJ/mol
- IE₃ = 2745 kJ/mol

### Step 2: Identify the Type of Elements
- **Element P**: The first ionization energy (IE₁) is relatively low (495.8 kJ/mol), indicating that it is likely an alkali metal (group 1). The large jump between IE₁ and IE₂ (from 495.8 to 4582 kJ/mol) suggests that after removing one electron, the element achieves a stable noble gas configuration.

- **Element Q**: The first ionization energy is higher (737.7 kJ/mol), and the second ionization energy (1451 kJ/mol) is also significantly higher than the first, indicating that Q is likely an alkaline earth metal (group 2). The large jump from IE₂ to IE₃ (from 1451 to 7733 kJ/mol) suggests that after removing two electrons, the element also achieves a stable configuration.

- **Element R**: The first ionization energy is moderate (577.5 kJ/mol), but the second and third ionization energies (1817.2 and 2745 kJ/mol) do not show a significant jump compared to P and Q. This suggests that R may not belong to the S block, as S block elements typically show a large increase in ionization energy after removing the first two electrons.

### Step 3: Conclusion on Element R
Given that the ionization energies of R do not show a significant increase after the first and second ionizations, it is likely that R belongs to the P block rather than the S block. This contradicts the assumption that R is an S block element.

### Final Answer
Thus, the incorrect option is related to element R being classified as an S block element based on its ionization energies.