The magnitude of a vector cannot be :

Options

A. positive
B. unity
C. negative
D. zero

Answer

To solve the question regarding the magnitude of a vector, we need to analyze the properties of vectors and their magnitudes step by step.

### Step-by-Step Solution:

1. **Understanding Vectors**:
- A vector is a quantity that has both magnitude and direction. Examples include displacement, velocity, and force.

2. **Magnitude of a Vector**:
- The magnitude of a vector is a measure of its size or length. It is always a non-negative value.

3. **Possible Values for Magnitude**:
- **Positive Magnitude**: A vector can have a positive magnitude. For example, a vector with a magnitude of 5 units is valid.
- **Unity Magnitude**: A vector can have a magnitude of 1, which is known as a unit vector. For instance, a unit vector in the direction of the x-axis can be represented as \( \hat{i} \) with a magnitude of 1.
- **Zero Magnitude**: A vector can have a magnitude of zero, which is referred to as a null vector. This means the vector has no length and does not point in any direction.

4. **Negative Magnitude**:
- The magnitude of a vector cannot be negative. Magnitude is a measure of size, and size cannot be negative. Therefore, this option is not valid.

5. **Conclusion**:
- Based on the analysis, the only option that is not possible for the magnitude of a vector is negative magnitude. Thus, the correct answer is that the magnitude of a vector cannot be negative.

### Final Answer:
The magnitude of a vector cannot be negative.