The ionic radii of `Li^(+)`, `Be^(2+) and B^(3+)` follow the order:

Options

A. `Be^(2+) gt B^(3+) gt Li^(+)`
B. `Li^(+) gt B^(3+) gt Be^(2+) `
C. `B^(3+) gt Be^(2+) gt Li^(+)`
D. `Li^(+) gt Be^(2+) gt B^(3+) `

Answer

To determine the order of ionic radii for the ions \( Li^{+} \), \( Be^{2+} \), and \( B^{3+} \), we can follow these steps:

### Step 1: Identify the Ions
The ions we are considering are:
- \( Li^{+} \) (Lithium ion)
- \( Be^{2+} \) (Beryllium ion)
- \( B^{3+} \) (Boron ion)

### Step 2: Determine the Number of Electrons
Each of these ions is formed from their respective neutral atoms by losing electrons:
- Lithium (Li) has 3 electrons, so \( Li^{+} \) has 2 electrons.
- Beryllium (Be) has 4 electrons, so \( Be^{2+} \) has 2 electrons.
- Boron (B) has 5 electrons, so \( B^{3+} \) has 2 electrons.

Since all three ions have lost electrons and now have the same number of electrons (2), they are classified as isoelectronic species.

### Step 3: Understand Isoelectronic Species
Isoelectronic species are ions or atoms that have the same number of electrons. In this case, \( Li^{+} \), \( Be^{2+} \), and \( B^{3+} \) all have 2 electrons.

### Step 4: Analyze the Charge and Size Relationship
In isoelectronic species, the size of the ion is inversely related to the charge on the ion:
- \( Li^{+} \) has a +1 charge.
- \( Be^{2+} \) has a +2 charge.
- \( B^{3+} \) has a +3 charge.

As the positive charge increases, the effective nuclear charge experienced by the electrons also increases, pulling the electrons closer to the nucleus and resulting in a smaller ionic radius.

### Step 5: Order the Ionic Radii
Based on the increasing positive charge:
- \( Li^{+} \) will have the largest ionic radius because it has the least positive charge.
- \( Be^{2+} \) will be smaller than \( Li^{+} \) but larger than \( B^{3+} \).
- \( B^{3+} \) will have the smallest ionic radius due to the highest positive charge.

Thus, the order of ionic radii is:
\[ Li^{+} > Be^{2+} > B^{3+} \]

### Final Answer
The ionic radii of \( Li^{+} \), \( Be^{2+} \), and \( B^{3+} \) follow the order:
\[ Li^{+} > Be^{2+} > B^{3+} \]

---