In which specific branch of economics did the Indian economist Amartya Sen receive the Nobel Prize in Economic Sciences?

Introduction / Context:
Amartya Sen is one of India's most renowned economists and philosophers. He received the Nobel Prize in Economic Sciences in 1998 for his groundbreaking contributions that reshaped the way economists and policy makers think about welfare, poverty and social choice. This question asks you to identify the particular branch of economics for which he was honoured.

Given Data / Assumptions:

The economist in question is Amartya Sen, an Indian scholar of international repute.
He received the Nobel Prize in Economic Sciences in 1998.
The options list branches or themes within economics such as micro economics, welfare economics and growth models.
We assume the Nobel citation focused on a clearly described area of work.

Concept / Approach:
The Nobel Prize in Economic Sciences is awarded for major contributions that advance economic theory or its application. Amartya Sen's work centres on welfare economics and social choice theory, with deep analysis of poverty, inequality and human capabilities. Although his research touches several areas including famine theory and development economics, the Nobel citation specifically highlights his contributions to welfare economics. Therefore, welfare economics is the correct field among the options.

Step-by-Step Solution:
Step 1: Recognise that Amartya Sen is widely associated with the study of welfare, social choice, poverty and inequality in economics. Step 2: Recall that the Nobel committee mentioned his contributions to welfare economics in the official citation for the 1998 prize. Step 3: Examine the options and identify Welfare Economics as one of the listed fields. Step 4: Note that micro economics and growth models are broader or different themes and do not match the specific Nobel citation. Step 5: Conclude that the correct answer is Welfare Economics, as it captures the central focus of his Nobel winning research.

Verification / Alternative check:
To verify, remember that Amartya Sen worked extensively on measuring welfare and poverty, creating new indices and methods to evaluate how resources and opportunities are distributed in society. His ideas helped shape the concept of human development and influenced the Human Development Index used by the United Nations. All of this falls under welfare economics, which studies how economic policies affect social welfare. Micro economics and growth models are important but do not capture the main theme of his Nobel recognised work, confirming that welfare economics is the correct field.

Why Other Options Are Wrong:
Micro Economics: Although Sen used micro economic tools, the Nobel committee did not honour him specifically for general micro economics but for his deeper contributions to welfare concepts and social choice.
Economic Growth Model: He has influenced development thinking, but he is not primarily known for proposing a single new growth model that would qualify as the focus of the Nobel citation.
Input Output Model: This phrase refers more to work by economists like Wassily Leontief, not to Sen, so this option does not describe his recognised contribution.

Common Pitfalls:
Examinees sometimes see the word economics and choose a broad category such as micro economics without considering the specific content of Sen's work. Others may mix him up with growth theorists or assume that winning a Nobel Prize automatically implies a contribution in growth modelling or macro economics. The key is to link his major achievements to subjects like welfare measurement, poverty analysis and social choice, which clearly place him in welfare economics. Developing this habit of matching names to their core areas helps avoid similar errors in other award related questions.

Final Answer:
Amartya Sen received the Nobel Prize in Economic Sciences for his contributions to Welfare Economics.