Which two are closest to one another in size ?

Options

A. `Li^(+) and Na^(+)`
B. `Be^(+2) and Mg^(+2)`
C. `Be^(+2) and Li^(-)`
D. `Li^(+) and Mg^(+2)`

Explanation

To solve the question of which two ions are closest to one another in size, we can follow these steps:

### Step 1: Identify the Ions
We are given four pairs of ions to compare:
1. Li⁺ and Na⁺
2. Be²⁺ and Mg²⁺
3. Be²⁺ and Li⁻
4. Li⁺ and Mg²⁺

### Step 2: Understand Ionic Sizes
Ionic size is influenced by several factors, including the charge of the ion and the number of electrons. Generally, cations (positively charged ions) are smaller than their parent atoms because they lose electrons, leading to a decrease in electron-electron repulsion and a greater effective nuclear charge on the remaining electrons.

### Step 3: Compare the Sizes of Ions
To determine which ions are closest in size, we can look up or recall the ionic radii of the ions involved:
- Li⁺: Approximately 76 picometers (pm)
- Na⁺: Approximately 102 pm
- Be²⁺: Approximately 31 pm
- Mg²⁺: Approximately 72 pm
- Li⁻: Approximately 152 pm

### Step 4: Analyze the Sizes
Now, we can analyze the sizes:
- Li⁺ (76 pm) vs. Na⁺ (102 pm): Difference of 26 pm
- Be²⁺ (31 pm) vs. Mg²⁺ (72 pm): Difference of 41 pm
- Be²⁺ (31 pm) vs. Li⁻ (152 pm): Difference of 121 pm
- Li⁺ (76 pm) vs. Mg²⁺ (72 pm): Difference of 4 pm

### Step 5: Conclusion
From the analysis, we see that the closest pair in size is:
- Li⁺ (76 pm) and Mg²⁺ (72 pm) with a difference of only 4 pm.

Thus, the answer to the question is:
**Li⁺ and Mg²⁺ are closest to one another in size.**

### Final Answer
The correct option is: **Li⁺ and Mg²⁺.**

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