Magnetization and its Definition:
Magnetization is a fundamental property of magnetic materials, which quantifies the degree to which a material becomes magnetized when subjected to an external magnetic field. It is often denoted by the letter M and is measured in units of Am².

Explanation of the Ratio:
The ratio mentioned in the question is the ratio of the magnetic moment to volume. Let's understand why this is the correct answer.

Magnetic Moment:
The magnetic moment of a material is a measure of its magnetic strength, indicating the tendency of the material to align its magnetic domains in the presence of an external magnetic field. It is denoted by the symbol µ and is measured in units of Am².

Area and Volume:
In the context of this question, the area refers to the cross-sectional area of the material, while the volume refers to the total volume of the material.

Magnetic Flux Density:
Magnetic flux density, often denoted by the symbol B, is a measure of the strength of a magnetic field. It represents the number of magnetic field lines passing through a given area. It is measured in units of Tesla (T).

Explanation of the Correct Answer (Option B):
The magnetization is defined by the ratio of the magnetic moment to volume (Magnetic moment / Volume). Here's why this is the correct answer:

1. Magnetic Moment:
- The magnetic moment of a material is a measure of its magnetic strength.
- It quantifies the ability of the material to generate a magnetic field.
- The larger the magnetic moment, the stronger the magnetic field generated by the material.

2. Volume:
- The volume of a material refers to the total amount of space occupied by the material.
- In the context of magnetization, it represents the amount of material available for magnetization.
- The larger the volume, the more material is available for magnetization.

3. Ratio of Magnetic Moment to Volume:
- The ratio of magnetic moment to volume (Magnetic moment / Volume) quantifies the magnetization of a material.
- It represents the magnetic strength generated per unit volume of the material.
- A higher value of this ratio indicates a higher level of magnetization, i.e., the material becomes more strongly magnetized per unit volume.

Therefore, the correct answer is option B: Magnetic moment to volume (Magnetic moment / Volume).