Which of the following physical quantity unit is not a fundamental unit?

Options

A. Length
B. Mass
C. Magnetic field
D. Current

Answer

To solve the question of which physical quantity unit is not a fundamental unit, we can follow these steps:

### Step 1: Understand Fundamental Quantities
Fundamental quantities are the basic physical quantities that are not derived from other quantities. There are seven fundamental quantities recognized in the International System of Units (SI).

### Step 2: List the Fundamental Quantities
The seven fundamental quantities are:
1. Mass (m)
2. Length (L)
3. Time (T)
4. Electric Current (I)
5. Temperature (T)
6. Amount of Substance (n, in moles)
7. Luminous Intensity (Iv)

### Step 3: Analyze the Options
Now we will analyze the options given in the question:
- Length: This is a fundamental quantity.
- Mass: This is also a fundamental quantity.
- Current: This is a fundamental quantity as well.
- Magnetic Field: This is not a fundamental quantity; it is derived from other quantities (specifically, it is derived from electric current and length).

### Step 4: Identify the Non-Fundamental Quantity
From the analysis, we can see that the only option that is not a fundamental quantity is the magnetic field.

### Conclusion
Therefore, the correct answer is that the unit corresponding to the magnetic field is not a fundamental unit.

### Final Answer
The correct option is **C: Magnetic Field**.

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