Macroeconomics is a branch of economics that deals with the overall performance, structure, behavior, and decision-making of an economy as a whole. It focuses on the aggregate measures of the economy and analyzes the factors that influence economic growth, unemployment, inflation, and other macroeconomic indicators. In this context, let's analyze the options given:

1. Gross Domestic Product (GDP):
GDP is the total value of all final goods and services produced within a country's borders during a given period. It is a crucial macroeconomic indicator that measures the overall economic activity and output of a country. Changes in GDP reflect the growth or contraction of the economy.

2. National Income:
National income refers to the total income earned by individuals, businesses, and the government in a country during a specific period. It includes wages, salaries, profits, rent, and interest. National income is an important measure of the overall economic well-being of a nation.

3. Inflation:
Inflation is the rate at which the general level of prices for goods and services is rising and, consequently, the purchasing power of currency is falling. It is an essential macroeconomic concept as it affects the cost of living, saving, investment, and economic stability. Governments and central banks often take measures to manage inflation within acceptable limits.

4. Profits of a firm:
Profits of a firm fall under microeconomics, which focuses on individual economic agents such as households, firms, and markets. Microeconomics analyzes the behavior of these agents and how their interactions determine prices and quantities in specific markets.

5. Demand and supply:
Demand and supply are fundamental concepts in economics that apply to both microeconomics and macroeconomics. While microeconomics focuses on the behavior of individual consumers and firms in specific markets, macroeconomics examines aggregate demand and supply factors that influence the overall performance of the economy.

Based on the explanations above, we can conclude that options 1, 2, and 3 (Gross Domestic Product, National Income, and Inflation) fall under macroeconomics. These indicators and concepts are used to analyze and understand the overall performance and behavior of an economy as a whole. Therefore, the correct answer is option 'C' - 1, 2, and 3.