Which of the following order of radii is correct?

Options

A. `Li lt Be lt Mg`
B. `H^(+) lt Li^(+) lt H^(-)`
C. `O lt F lt Ne`
D. `Li lt Na lt K lt Ca lt Rb`

Explanation

To determine the correct order of atomic radii from the given options, we need to understand the trends in atomic radii in the periodic table. Here’s a step-by-step solution:

### Step 1: Understand the Trends in Atomic Radii
- **Atomic Radius Increases Down a Group**: As we move down a group in the periodic table, the atomic radius increases due to the addition of electron shells.
- **Atomic Radius Decreases Across a Period**: As we move from left to right across a period, the atomic radius decreases because of the increasing nuclear charge, which pulls the electrons closer to the nucleus.

### Step 2: Analyze Each Option
1. **Option A: Lithium (Li), Beryllium (Be), Magnesium (Mg)**
- Lithium is in Group 1, Beryllium in Group 2, and Magnesium in Group 2.
- As we move from Li to Be to Mg, we are moving across a period, so the atomic radius should decrease.
- **Conclusion**: This order is incorrect (Li > Be > Mg).

2. **Option B: H⁺, Li⁺, H⁻**
- H⁺ is a cation (smaller than H), Li⁺ is also a cation, and H⁻ is an anion (larger than H).
- H⁺ has 1 proton, Li⁺ has 3 protons (pulling 2 electrons), and H⁻ has 1 proton (pulling 2 electrons).
- Since Li⁺ has a higher nuclear charge than H⁻, it will be smaller than H⁻.
- **Conclusion**: The order is correct (H⁺ < Li⁺ < H⁻).

3. **Option C: Oxygen (O), Fluorine (F), Neon (Ne)**
- Oxygen is in Group 16, Fluorine in Group 17, and Neon in Group 18.
- As we move from O to F to Ne, the atomic radius decreases across the period.
- Neon, being a noble gas, has a larger atomic radius due to van der Waals forces, but it is still smaller than O and F.
- **Conclusion**: This order is incorrect (O > F > Ne).

4. **Option D: Lithium (Li), Sodium (Na), Potassium (K), Calcium (Ca), Rubidium (Rb)**
- Li, Na, K are in Group 1, and Ca is in Group 2.
- As we move down the group, the atomic radius increases.
- However, Ca (Group 2) has a smaller atomic radius than K (Group 1), making this order incorrect.
- **Conclusion**: This order is incorrect (Li < Na < K < Ca < Rb).

### Final Answer
The correct order of atomic radii is given in **Option B: H⁺ < Li⁺ < H⁻**.