A protoxin is

Options

A. a primitive toxin
B. a denatured toxin
C. toxin produced by protozoa
D. inactive toxin

Answer

To solve the question "A protoxin is," we need to analyze the given options and determine the correct definition of a protoxin.

### Step-by-Step Solution:

1. **Understanding the Term "Protoxin":**
- A protoxin is a precursor to a toxin. It is not active in its original form and requires a specific change to become toxic.

2. **Evaluating the Options:**
- **Option A: Primitive toxin** - This suggests that protoxins are basic or early forms of toxins, which is not accurate.
- **Option B: Denatured toxin** - Denatured refers to a protein that has lost its natural structure, but this does not specifically define a protoxin.
- **Option C: Toxin produced by protozoa** - This implies that protoxins are exclusively produced by protozoa, which is incorrect as protoxins can be produced by various organisms.
- **Option D: Inactive toxin** - This accurately describes a protoxin, as it is an inactive form that becomes active under specific conditions (like changes in temperature or pH).

3. **Conclusion:**
- Based on the analysis, the correct answer is **Option D: Inactive toxin**. Protoxins are inactive until they undergo a transformation that activates them.