Three elements X , Y and Z have atomic numbers 19 , 37 and 55 respectively . Then the correct statement (s) is / are

Options

A. Their ionization potential would increase with increasing atomic number.
B. Y would have an ionization potential between those of X and Z.
C. Z would have the highest ionization potential.
D. Y would have the highest ionization potential.

Explanation

To solve the question regarding the elements X, Y, and Z with atomic numbers 19, 37, and 55 respectively, we will follow these steps:

### Step 1: Identify the Elements
- The atomic number 19 corresponds to Potassium (K).
- The atomic number 37 corresponds to Rubidium (Rb).
- The atomic number 55 corresponds to Cesium (Cs).

### Step 2: Write the Electronic Configurations
- For Potassium (K, atomic number 19): The electronic configuration is \( 1s^2 2s^2 2p^6 3s^1 \) or simplified as \( 2, 8, 8, 1 \).
- For Rubidium (Rb, atomic number 37): The electronic configuration is \( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 \) or simplified as \( 2, 8, 18, 8, 1 \).
- For Cesium (Cs, atomic number 55): The electronic configuration is \( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4p^6 5s^1 \) or simplified as \( 2, 8, 18, 18, 8, 1 \).

### Step 3: Determine the Group
- All three elements (K, Rb, Cs) have one electron in their outermost shell (valence shell), indicating they belong to Group 1 (alkali metals).

### Step 4: Analyze Ionization Potential
- Ionization potential (or ionization energy) is the energy required to remove an electron from an atom.
- As we move down Group 1 from K to Rb to Cs, the ionization potential decreases due to the increasing distance of the outermost electron from the nucleus (more electron shells).

### Step 5: Evaluate the Statements
1. **Statement 1**: "The ionization potential would increase with increasing atomic number."
- This statement is **incorrect** because the ionization potential decreases as we go down the group.

2. **Statement 2**: "Y would have an ionization potential between those of X and Z."
- This statement is **correct** because as we move down the group, the ionization potential decreases, so K (X) has the highest, followed by Rb (Y), and then Cs (Z).

3. **Statement 3**: "Z would have the highest ionization potential."
- This statement is **incorrect** because Cs (Z) has the lowest ionization potential among the three.

### Conclusion
The correct statement is:
- **Statement 2**: Y would have an ionization potential between those of X and Z.