Identify the correct order in which the covalent radius of the following elements increases ?
(i) `Ti` (ii) `Ca`
(iii) `Sc`

Options

A. (I) ,II,III
B. III,II,I
C. III,I,III
D. I,III,II

Explanation

To determine the correct order in which the covalent radius of the elements titanium (Ti), calcium (Ca), and scandium (Sc) increases, we need to consider their positions in the periodic table and the trends in atomic size.

### Step-by-Step Solution:

1. **Identify the Group and Period of Each Element:**
- Titanium (Ti) is in Group 4 and Period 4.
- Scandium (Sc) is in Group 3 and Period 4.
- Calcium (Ca) is in Group 2 and Period 4.

2. **Understand the Trend in Covalent Radius:**
- As we move from left to right across a period in the periodic table, the covalent radius generally decreases. This is because the effective nuclear charge increases, pulling the electrons closer to the nucleus and reducing the size of the atom.
- Conversely, as we move down a group, the covalent radius increases due to the addition of electron shells.

3. **Compare the Elements:**
- Since all three elements are in the same period (Period 4), we can directly compare their covalent radii based on their group numbers.
- Calcium (Group 2) is to the left of both Scandium (Group 3) and Titanium (Group 4), meaning it will have the largest covalent radius.
- Scandium (Group 3) is to the left of Titanium (Group 4), so it will have a larger covalent radius than Titanium.

4. **Establish the Order:**
- From the above comparisons, we can conclude:
- Titanium (Ti) has the smallest covalent radius.
- Scandium (Sc) has a larger covalent radius than Titanium but smaller than Calcium.
- Calcium (Ca) has the largest covalent radius.

5. **Final Order of Increasing Covalent Radius:**
- Therefore, the correct order in which the covalent radius increases is:
- Ti < Sc < Ca

### Final Answer:
The correct order of increasing covalent radius is: **Ti < Sc < Ca**