Many elements are found in living organisms either free or in the form of compounds. One of the following is not found in living organisms.

Options

A. Silicon
B. Magnesium
C. Iron
D. Sodium

Answer

To solve the question regarding which element is not found in living organisms, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which of the given elements is not found in living organisms, either in free form or as part of compounds.

2. **Identify Common Elements in Living Organisms**:
- Common elements found in living organisms include:
- **Hydrogen (H)**: Approximately 0.5% of the human body.
- **Carbon (C)**: Approximately 18.5% of the human body.
- **Oxygen (O)**: Approximately 65% of the human body.
- **Nitrogen (N)**: Approximately 3.3% of the human body.
- **Sulfur (S)**: Approximately 0.3% of the human body.
- **Sodium (Na)**: Approximately 0.2% of the human body.
- **Calcium (Ca)**: Approximately 1.5% of the human body.
- **Magnesium (Mg)**: Approximately 0.1% of the human body.

3. **Consider the Element in Question**:
- The element in question is **Silicon (Si)**. It is known to be present in the earth's crust but is found in negligible amounts in living organisms.

4. **Conclusion**: Since silicon is either absent or present in very minimal amounts in living organisms, it is the correct answer to the question.

5. **Final Answer**: The element that is not found in living organisms is **Silicon**.