Choose the correct statement

Options

A. Ionisation energy and electron affinity increases across a period
B. Ionisation energy increases but electron affinity decreases along a period
C. Ionisation energy decreases but electron affinity increases
D. Both decreases along a period

Answer

To solve the question, we need to analyze the statements regarding ionization energy and electron affinity as we move across a period in 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.
- As we move from left to right across a period, the ionization energy generally increases. This is due to the increase in effective nuclear charge, which means that the nucleus has a stronger attraction on the electrons, making it harder to remove an electron.

2. **Understanding Electron Affinity**:
- Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gaseous state.
- Similar to ionization energy, as we move from left to right across a period, electron affinity tends to increase. This is because the added electron experiences a stronger attraction to the positively charged nucleus due to increased nuclear charge.

3. **Evaluating the Statements**:
- The first statement claims that both ionization energy and electron affinity increase across the period. This is consistent with our understanding of periodic trends.
- The second statement claims that ionization energy increases while electron affinity decreases. This is incorrect as both increase.
- The third statement claims that ionization energy decreases while electron affinity increases. This is also incorrect as ionization energy increases.
- The fourth statement claims that both ionization energy and electron affinity decrease. This is incorrect as both increase.

4. **Conclusion**:
- The correct statement is the first one: "Ionization energy and electron affinity increase across the period."

### Final Answer:
The correct statement is: **Ionization energy and electron affinity increase across the period.**