Directions: Read the Assertion (A) and Reason (R) carefully and choose the correct alternative. Assertion (A): There is no fully successful and widely available vaccine for AIDS. Reason (R): The virus that causes AIDS shows rapid changes in its genetic material, making vaccine development very difficult.

Introduction / Context:
This Assertion and Reason question relates to human health, immunology, and virology. It specifically concerns AIDS, which is caused by infection with the Human Immunodeficiency Virus. The question checks whether you know about the status of vaccine development for AIDS and understand why creating such a vaccine is scientifically challenging. It is important to treat this as a conceptual question rather than as medical advice.

Given Data / Assumptions:

• Assertion (A) states that there is no successful, widely used vaccine for AIDS.
• Reason (R) states that the AIDS virus changes its genetic code frequently.
• The virus responsible for AIDS is HIV, an RNA virus that uses reverse transcriptase.
• We consider the general statement that despite research, there is no standard, globally used preventive vaccine for AIDS.

Concept / Approach:
Viruses can mutate, that is, change their genetic material. HIV in particular has a very high mutation rate due to the error prone nature of reverse transcriptase and the presence of many viral variants, even within a single infected person. Vaccine development usually relies on having stable viral antigens so the immune system can recognise them. When the virus changes rapidly, antigens keep shifting, making it hard to design a single vaccine that works reliably across all strains and over time.

Step-by-Step Solution:
Step 1: Many diseases, such as measles or polio, have well established vaccines that are part of national immunisation programmes. Step 2: For AIDS, however, despite decades of intensive research, there is no globally accepted, fully successful vaccine that is routinely given to the general population for prevention. Step 3: Therefore Assertion (A) is considered true in the context of exam level general knowledge. Step 4: Reason (R) states that the AIDS virus changes its genetic code. HIV is known for its high rate of mutation and formation of many sub types and quasispecies, causing antigenic variation. Step 5: This rapid genetic change leads to frequent changes in surface proteins that would be targeted by vaccines. As a result, an immune response built against one variant may not protect effectively against another. Step 6: Therefore Reason (R) is also true and it provides a strong scientific explanation for why vaccine development for HIV and AIDS is extremely difficult.

Verification / Alternative check:
Scientific literature and health education materials often mention that HIV has a high mutation rate and that this is one of the main reasons for the lack of a simple, widely used preventive vaccine. While there are experimental vaccine candidates and ongoing trials, there is still no universal, standard vaccine programme for AIDS like there is for diseases such as polio or measles. This supports the truth of both statements and the causal link given in the Reason.

Why Other Options Are Wrong:
Options that treat the Assertion as false would imply that an effective vaccine is already widely available, which is not correct at present. Options that deny the high mutation rate of HIV contradict well known virology facts. Options claiming that the Reason does not explain the Assertion ignore the central role that viral variation plays in vaccine design challenges.

Common Pitfalls:
Students sometimes confuse preventive vaccines with treatment options like antiretroviral therapy, which are drugs and not vaccines. Others may have heard about vaccine research and mistakenly assume that a final product already exists for public use. It is important to separate experimental trials and partial results from a widely implemented, proven vaccine programme.

Final Answer:
Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), so the correct option is Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).