Small clay particles hold calcium, potassium and magnesium ions because surfaces of clay particles are

Options

A. smooth
B. covered with tiny crevices
C. negatively charged
D. waxy

Answer

### Step-by-Step Solution:

1. **Understanding Clay Composition**:
- Clay is primarily composed of small particles that can hold various ions. It often contains organic matter, which is a mix of carbon, hydrogen, and oxygen.

**Hint**: Consider what materials make up clay and their properties.

2. **Disassociation of Organic Acids**:
- The organic matter in clay can disassociate into organic acids. This process results in the formation of negatively charged particles.

**Hint**: Think about how organic acids behave in a mixture and what ions they might release.

3. **Charge of Clay Particles**:
- Due to the disassociation of organic acids, the surfaces of clay particles become negatively charged. This negative charge is crucial for the attraction of positively charged ions.

**Hint**: Recall the relationship between charge types—how do positive and negative charges interact?

4. **Attraction of Cations**:
- Positively charged ions (cations) such as calcium (Ca²⁺), potassium (K⁺), and magnesium (Mg²⁺) are attracted to the negatively charged surfaces of the clay particles.

**Hint**: Identify the charges of the specific ions mentioned in the question and how they relate to the clay's charge.

5. **Ionic Retention**:
- The negatively charged surfaces of clay particles effectively hold onto these cations, allowing the clay to retain essential nutrients like calcium, potassium, and magnesium.

**Hint**: Consider the importance of nutrient retention in soil and how it affects plant growth.

### Final Answer:
Small clay particles hold calcium, potassium, and magnesium ions because the surfaces of clay particles are negatively charged, which attracts and retains these positively charged ions.