Dentist use the salts of alginic acid to take the measurement of dentury. These are obtained from:

Options

A. Red algae
B. Bacteria
C. Brown algae
D. Diatom

Answer

To solve the question regarding the source of alginic acid used by dentists for taking measurements of dentures, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Context**: The question asks about the source of alginic acid salts used in dentistry.

2. **Understand Alginic Acid**: Alginic acid is a substance that is commonly used in various applications, including dentistry, due to its properties as a thickening agent and its ability to form gels.

3. **Explore the Types of Algae**: Alginic acid is derived from algae. Algae can be classified into three main groups based on their pigments:
- Green Algae (Chlorophyll A and B)
- Red Algae (Chlorophyll A and D, with phycoerythrin)
- Brown Algae (Chlorophyll A and C, with fucoxanthin)

4. **Focus on Brown Algae**: The key to the question lies in identifying which type of algae contains alginic acid. It is known that alginic acid is specifically found in the cell walls of brown algae.

5. **Confirm the Source**: Since the question is about the source of alginic acid, we can conclude that brown algae are the organisms from which alginic acid is obtained.

6. **Final Answer**: Therefore, the correct answer to the question is that alginic acid salts used by dentists are obtained from **brown algae**.