Decreasing ionisation potential for K, Ca & Ba is

Options

A. Ba gt K gt Ca
B. `Ca gt Ba gt K`
C. K gt Ba gt Ca
D. K gt Ca gt Ba

Answer

To determine the decreasing order of ionization potential for potassium (K), calcium (Ca), and barium (Ba), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers**:
- Potassium (K) has an atomic number of 19.
- Calcium (Ca) has an atomic number of 20.
- Barium (Ba) has an atomic number of 56.

2. **Write the Electronic Configurations**:
- Potassium (K): [Ar] 4s¹
- Calcium (Ca): [Ar] 4s²
- Barium (Ba): [Xe] 6s²

3. **Determine the Period and Group of Each Element**:
- Potassium (K) is in Period 4, Group 1.
- Calcium (Ca) is in Period 4, Group 2.
- Barium (Ba) is in Period 6, Group 2.

4. **Understand the Trend of Ionization Potential**:
- Ionization potential generally decreases down a group due to the increase in the number of electron shells, which reduces the effective nuclear charge felt by the outermost electrons.
- Ionization potential generally increases across a period due to the increase in nuclear charge (more protons) which holds the electrons more tightly.

5. **Compare the Ionization Potentials**:
- Between K and Ca: Since both are in the same period, Ca has a higher ionization potential than K due to the increased nuclear charge.
- Between Ca and Ba: Ba is below Ca in the same group (Group 2), so Ba will have a lower ionization potential than Ca due to the additional electron shell.
- Between K and Ba: K is in Period 4 while Ba is in Period 6, thus Ba will have a lower ionization potential than K.

6. **Establish the Decreasing Order**:
- From the comparisons, we can conclude:
- Ca > K > Ba

### Final Answer:
The decreasing order of ionization potential is: **Ca > K > Ba**