When a ferromagnetic substance is placed in a magnetic field, it becomes a permanent magnet because:

all the domains get oriented in the direction of the magnetic field

The correct answer is option 1. all the domains get oriented in the direction of the magnetic field.

Magnetic domains are small regions within a ferromagnetic material where the magnetic moments (spins) of atoms are aligned in the same direction. In an unmagnetized state, these domains are oriented randomly throughout the material, so their magnetic effects cancel each other out, resulting in no net magnetism.

Behavior of Magnetic Domains in an External Magnetic Field:

When a ferromagnetic substance is exposed to an external magnetic field, the field exerts a force on the magnetic moments within the domains.

Alignment of Domains: The magnetic moments within the domains start to align with the direction of the external magnetic field. This alignment reduces the magnetic energy of the system, making it more stable.

As the strength of the external field increases, more domains align with the field. In some cases, smaller domains may also merge with larger ones that are aligned with the field, further increasing the net magnetization of the material.

Permanent Magnetization: Once a sufficient number of domains have aligned in the direction of the magnetic field, the material becomes magnetized.

Retaining Magnetization: After the external magnetic field is removed, many of the domains remain in their aligned state, which gives the material a net magnetic moment, making it a permanent magnet. The material retains this magnetization because the aligned domains tend to stay in their low-energy configuration.

Key Concepts:

Domain Alignment: The process of domains aligning with the external magnetic field is crucial for the material to become magnetized.

Hysteresis: The tendency of the domains to remain aligned even after the external field is removed is called hysteresis. This is what makes the magnetization permanent.

Saturation Magnetization: When nearly all the domains are aligned with the magnetic field, the material reaches a state called saturation, where further increases in the external field do not significantly increase the magnetization.

Why the Correct Answer is Option 1:

All the domains get oriented in the direction of the magnetic field": This statement accurately describes the process that leads to the formation of a permanent magnet. The alignment of the domains in the direction of the applied magnetic field is what results in a strong, lasting magnetic effect.
 

Opposite Alignment (Option 2) would not lead to magnetization but rather demagnetization.

Random Orientation (Option 3) would cancel out the magnetic effects, resulting in no net magnetization.

Unaffected Domains (Option 4) implies that the material would not respond to the magnetic field, which contradicts the behavior of ferromagnetic substances.

Summary:

The formation of a permanent magnet in a ferromagnetic substance occurs because the magnetic domains within the material align in the direction of the applied magnetic field. This alignment persists even after the external field is removed, leading to permanent magnetization. This is why Option 1 is the correct answer.