Who among the following became the youngest Prime Minister of India, assuming office at the age of about forty years?

Introduction / Context:
Questions about firsts, superlatives and key biographical facts of Indian leaders are very common in general knowledge and polity exams. The identity of the youngest Prime Minister of India is one such fact. This question asks you to recall who became Prime Minister at a relatively young age, around forty years old, and is therefore known as the youngest person to hold that office in India.

Given Data / Assumptions:

• We are looking for the youngest Prime Minister of India at the time of assuming office.
• The options include Atal Bihari Vajpayee, Rajiv Gandhi, Morarji Desai and Indira Gandhi.
• We assume familiarity with the broad time periods during which these leaders served as Prime Minister.
• The answer is based on age at the start of their term.

Concept / Approach:
Rajiv Gandhi became Prime Minister of India in 1984 following the assassination of Indira Gandhi. At that time he was about forty years old, making him the youngest Prime Minister in Indian history. The other leaders listed in the options were older when they assumed office. Therefore, the approach is to match the known fact youngest Prime Minister with the correct name, Rajiv Gandhi, and reject the other options by recalling that they served at more advanced ages.

Step-by-Step Solution:
Step 1: Recall that Rajiv Gandhi took office as Prime Minister in 1984 at around forty years of age. Step 2: Recognise that he is frequently mentioned in exam material as the youngest Prime Minister of India. Step 3: Atal Bihari Vajpayee became Prime Minister at a much older age and is not associated with being the youngest. Step 4: Morarji Desai was in his seventies when he became Prime Minister, clearly not a candidate for youngest Prime Minister. Step 5: Indira Gandhi served as Prime Minister earlier and was older than Rajiv Gandhi at the time she took office. Step 6: Therefore, among the given options, Rajiv Gandhi is the correct answer.

Verification / Alternative check:
To verify, you can link Rajiv Gandhi’s age and period of office with other historical events. His tenure saw the mid 1980s technology and economic changes, and he was often described in newspapers and books as a relatively young and modern leader compared to earlier prime ministers. Standard reference books and exam guides explicitly state that Rajiv Gandhi holds the record as the youngest Prime Minister of India. This repeated mention in multiple sources confirms that option B is correct and that the other names do not fit this description.

Why Other Options Are Wrong:
Option A: Atal Bihari Vajpayee became Prime Minister much later in life and is not known as the youngest Prime Minister.

Option C: Morarji Desai was significantly older and is associated with being one of the oldest prime ministers rather than the youngest.

Option D: Indira Gandhi, though a path breaking woman leader, did not hold the record for being the youngest Prime Minister when she assumed office.

Common Pitfalls:
A common mistake is to focus on who served earlier rather than on who was younger at the time of assuming office. For example, some may think that an earlier prime minister must have been younger simply because they came first, but age at the time of oath taking is the relevant factor. Another pitfall is to mix up the superlatives youngest and first, as with first woman Prime Minister or first non Congress Prime Minister. Carefully distinguishing these categories in your memory helps avoid confusion and ensures that you pick Rajiv Gandhi for youngest Prime Minister without hesitation.

Final Answer:
Rajiv Gandhi.