Consider the following statement
I.Transition element have almost same ionisation energy
II.Alkali metals lowest and inert gases have the highest ionisation energy in a period
III.Among all known elements He has the highest and Cs has the lowest ionisation energy
Select the correct statement

Options

A. I and II
B. I and III
C. II and III
D. All of these

Answer

To determine which statements are correct, we will analyze each one step by step.

### Step 1: Analyze Statement I
**Statement I:** Transition elements have almost the same ionization energy.

- **Explanation:** Transition metals have similar electron configurations, which leads to similar ionization energies. The presence of d-electrons contributes to the stability of these elements, resulting in relatively close ionization energy values across the transition series. Thus, this statement is **correct**.

### Step 2: Analyze Statement II
**Statement II:** Alkali metals have the lowest and inert gases have the highest ionization energy in a period.

- **Explanation:** Alkali metals (Group 1) indeed have the lowest ionization energies in their respective periods due to their single valence electron, which is easily removed. In contrast, noble gases (inert gases) have full valence shells, making them very stable and requiring a significant amount of energy to remove an electron. Therefore, this statement is also **correct**.

### Step 3: Analyze Statement III
**Statement III:** Among all known elements, He has the highest and Cs has the lowest ionization energy.

- **Explanation:** Helium (He) has the highest ionization energy among all elements because it has a very small atomic size and a full outer shell, making it very stable. On the other hand, cesium (Cs) has the lowest ionization energy due to its large atomic size and the presence of only one valence electron that is far from the nucleus. Thus, this statement is also **correct**.

### Conclusion
All three statements are correct.

### Final Answer:
All statements I, II, and III are correct.

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