The four elements that make up 99% of all elements found in a living system are
(a) CHOS
(b) CHOP
(c) CHON
(d) CNOP

Options

A. CHOS
B. CHOP
C. CHON
D. CNOP.

Answer

To solve the question regarding the four elements that make up 99% of all elements found in a living system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the four primary elements that constitute the majority of elements in living organisms.

2. **Identify Major Biomolecules**: Recognize that the major biomolecules in living systems include carbohydrates, proteins, lipids, and nucleic acids.

3. **List Common Elements in Biomolecules**: The primary elements that are found in these biomolecules are:
- **Carbon (C)**: A fundamental building block for all organic molecules.
- **Hydrogen (H)**: Often bonded to carbon and is part of water and organic compounds.
- **Oxygen (O)**: Essential for respiration and a component of water and organic molecules.
- **Nitrogen (N)**: A key component of amino acids (the building blocks of proteins) and nucleic acids (DNA and RNA).

4. **Evaluate the Options**:
- (a) CHOS: This includes Carbon, Hydrogen, Oxygen, and Sulfur. Sulfur is not one of the four major elements.
- (b) CHOP: This includes Carbon, Hydrogen, Oxygen, and Phosphorus. Phosphorus is also not one of the four major elements.
- (c) CHON: This includes Carbon, Hydrogen, Oxygen, and Nitrogen. This matches our identified elements.
- (d) CNOP: This includes Carbon, Nitrogen, Oxygen, and Phosphorus. Phosphorus is not one of the four major elements.

5. **Select the Correct Answer**: Based on the evaluation, the correct answer is (c) CHON, as it contains the four major elements that make up 99% of all elements found in living systems.

### Final Answer:
(c) CHON