Active Immunity:

Active immunity is the immunity that develops in the body after exposure to a pathogen (bacteria, virus, or any other infectious agent) or after taking a vaccine. It is called active immunity because the body’s immune system actively responds to the pathogen or vaccine by producing antibodies, which are specific proteins that bind to the pathogen and neutralize it.

Mechanism:

- The immune system recognizes the pathogen or vaccine as foreign and activates the B-cells and T-cells.
- B-cells produce specific antibodies that bind to the pathogen and neutralize it.
- T-cells destroy the infected cells that harbor the pathogen.
- Once the infection is cleared, some of the B-cells and T-cells remain in the body as memory cells, which can quickly recognize and respond to the same pathogen if it enters the body again.

Duration:

- Active immunity can last for a long time, sometimes for a lifetime, depending on the type of pathogen or vaccine.

Examples:

- Active immunity is developed after recovery from infections like chickenpox, measles, mumps, and rubella.
- It is also developed after vaccination against infectious diseases like polio, hepatitis B, influenza, and human papillomavirus (HPV).

Advantages:

- Active immunity is a natural and long-lasting immunity that protects the body against a wide range of infectious agents.
- It is also cost-effective, as it does not require frequent administration of vaccines or drugs.

Disadvantages:

- Active immunity takes time to develop, sometimes weeks or months, which can be fatal in some cases.
- It may not be effective against new strains or mutations of the pathogen.

Conclusion:

Active immunity is the most effective and natural way of developing immunity against infectious agents. It protects the body against a wide range of pathogens and can last for a lifetime. Vaccination is a safe and effective way of developing active immunity without the risk of contracting the disease.

First, you should know one thing that is
ACTIVE immunity is a natural immunity & long lasting. In this type our own cell recognize the antigen & synthesis the antibiotics. It was remain even the body was recovered from the disease.
But in PASSIVE immunity the antibiotics were obtained from outside. It never be a longer time in our body.
so the a each correct option is (B)