Read the passage carefully and answer the questions given below.

Our immune system plays the major role in preventing diseases when we are exposed to disease-causing agents. Immunity is of two types: (i) Innate immunity and (ii) Acquired immunity. The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies. The immune system also plays an important role in allergic reactions, auto-immune diseases and organ transplantation. The primary lymphoid organs are bone marrow and thymus. The secondary lymphoid organs are spleen, lymph nodes, tonsils, Peyer's patches of small intestine and appendix. There is lymphoid tissue also located within the lining of the major tracts (respiratory, digestive and urogenital tracts) called mucosa associated lymphoid tissue (MALT). It is important to note that HIV/AIDS is not spread by mere touch or physical contact it spreads only through body fluids. AIDS has no cure, prevention is the best option. Adolescence is accompanied by several biological and behavioural changes and surveys and statistics show that use of drugs and alcohol has been on the rise especially among the youth. Factors associated with drug and alcohol abuse among adolescents are a child's natural curiosity, stress, the perception among youth that it is 'cool' or progressive to smoke, media exposure and an unstable or unsupportive family structures and peer pressure. It is best to identify the situations that may push an adolescent towards use of drugs or alcohol, and to take remedial measures well in time.

Active immunization is most suitable method for:

Natural infection

The correct answer is Option (2) → Natural infection 

Active immunization is the process where the body's own immune system is stimulated to produce antibodies and memory cells against a specific antigen. This provides long-term protection. This can happen naturally or artificially.

• Natural infection: This is a form of natural active immunity. When a person recovers from a disease (like chickenpox or measles), their body has been exposed to the pathogen and has produced memory cells, resulting in long-lasting immunity. Therefore, natural infection is a mechanism of active immunization.
• Exposure to snake venom: This requires passive immunization. Snake venom acts quickly, and the body doesn't have time to mount an active response. The treatment involves immediately administering an antivenom (which contains pre-formed antibodies) to neutralize the venom.
• Deadly microbe infection: While active immunity can be developed against any microbe, if the infection is deadly, the person needs immediate protection. This would typically be a situation for passive immunization (like an injection of immunoglobulins) or immediate medical intervention, not waiting for the body to build active immunity. However, prevention of a deadly microbe infection is the main purpose of vaccination (artificial active immunity). Since the option specifies infection and the need for immediate action is implied by "deadly," it's less suitable than natural infection for defining the most suitable method of active immunization.
• Protection of fetus in the womb: This is an example of natural passive immunity. Antibodies (IgG) cross the placenta from the mother to the fetus, providing the fetus with temporary, immediate protection.

Conclusion: Natural infection is the most direct and clearest example of the body's own immune system creating long-term defense, which is the definition of active immunity. The most suitable method for active immunization among the options is Natural infection.