Among the elements Ca,Mg,P and Cl the order of decreasing atomic radii is

Options

A. `CagtMggtPgtCl`
B. `PgtClgtCagtMg`
C. `MggtCagtClgtP`
D. `ClgtPgtMggtCa`

Answer

To determine the order of decreasing atomic radii among the elements Ca (Calcium), Mg (Magnesium), P (Phosphorus), and Cl (Chlorine), we need to consider the periodic trends in atomic radii.

### Step-by-Step Solution:

1. **Identify the Groups and Periods**:
- Calcium (Ca) is in Group 2 and Period 4.
- Magnesium (Mg) is in Group 2 and Period 3.
- Phosphorus (P) is in Group 15 and Period 3.
- Chlorine (Cl) is in Group 17 and Period 3.

2. **Understand the Trend in Atomic Radii**:
- Atomic radii generally decrease across a period (from left to right) due to increasing nuclear charge, which pulls electrons closer to the nucleus.
- Atomic radii generally increase down a group due to the addition of electron shells.

3. **Compare the Elements**:
- **Calcium (Ca)**: Being in Period 4, it has a larger atomic radius than elements in Period 3 because it has an additional electron shell.
- **Magnesium (Mg)**: In Period 3 and Group 2, it has a larger atomic radius than both phosphorus and chlorine, as it is to the left of them in the same period.
- **Phosphorus (P)**: Also in Period 3 but in Group 15, it has a smaller atomic radius than magnesium due to the increase in nuclear charge.
- **Chlorine (Cl)**: In Period 3 and Group 17, it has the smallest atomic radius among these elements because it is the furthest to the right in Period 3.

4. **Order the Elements Based on Atomic Radii**:
- From largest to smallest atomic radius: **Ca > Mg > P > Cl**.

### Final Answer:
The order of decreasing atomic radii among the elements Ca, Mg, P, and Cl is:
**Ca > Mg > P > Cl**.