Choose the correct order of ionization energy for the following species. 

Options

A. `Sc gt La gt Y`
B. `Sc gt Y ~~ La`
C. `Sc gt Y gt La`
D. `Sc lt Y gt La`

Answer

To determine the correct order of ionization energy for the species scandium (Sc), yttrium (Y), and lanthanum (La), we can follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. Generally, ionization energy increases across a period and decreases down a group in the periodic table.

### Step 2: Identify the Elements and Their Positions
- Scandium (Sc) is in the 3D block (Period 4).
- Yttrium (Y) is in the 4D block (Period 5).
- Lanthanum (La) is in the 5D block (Period 6).

### Step 3: Analyze the Trends
1. **Down a Group**: As we move down a group in the periodic table, the number of electron shells increases, which leads to an increase in atomic size. This results in a decrease in ionization energy because the outermost electrons are further from the nucleus and experience less nuclear attraction.

2. **Across a Period**: As we move across a period from left to right, the atomic size decreases due to increasing nuclear charge, which leads to an increase in ionization energy.

### Step 4: Compare the Sizes of the Atoms
- Scandium (Sc) has the smallest atomic size among the three, as it is in the 3D block.
- Yttrium (Y) is larger than Scandium because it is in the 4D block.
- Lanthanum (La) is larger than Yttrium because it is in the 5D block.

### Step 5: Determine the Order of Ionization Energy
Based on the analysis:
- Scandium (Sc) will have the highest ionization energy due to its smaller size.
- Yttrium (Y) will have a lower ionization energy than Scandium but higher than Lanthanum.
- Lanthanum (La) will have the lowest ionization energy due to its larger size.

Thus, the correct order of ionization energy is:
**Scandium (Sc) > Yttrium (Y) > Lanthanum (La)**

### Final Answer
The correct order of ionization energy for the species is:
**Scandium > Yttrium > Lanthanum**

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