Money serves three primary functions: a medium of exchange, a unit of account, and a store of value. Among these, the medium of exchange is the most fundamental function, as it eliminates the need for the double coincidence of wants required in a barter system, thereby facilitating trade and economic transactions.

The informal sector consists of economic activities that are not regulated or protected by the state. It often includes small, family-owned businesses that operate with labor-intensive methods and rely on market-determined prices, playing a significant role in the employment landscape of developing nations.

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The book 'Choice of Techniques' was written by Nobel laureate Amartya Sen. It explores the economic theory regarding the selection of production techniques in developing economies, focusing on the trade-offs between labor-intensive and capital-intensive methods to maximize growth and employment.

Unemployment refers to the state where individuals who are willing and able to work cannot find employment. In a broader economic sense, it represents the failure of an economy to utilize its human resources fully. When labor is underutilized, the economy operates below its potential output, leading to a reduction in the total supply of goods and services available to the population.

The Law of Diminishing Returns is a fundamental concept in agricultural production. It explains that as you add more of a variable input (like fertilizer or labor) to a fixed resource (like land), the additional output gained from each subsequent unit of input will eventually decrease. This principle is vital for farmers to determine the optimal level of input application to maximize profit rather than just total yield.

In international trade theory, different measures of terms of trade were developed by economists. F.W. Taussig introduced the Gross Barter Terms of Trade. Dorance is associated with Income Terms of Trade. Jacob Viner developed the Single Factorial Terms of Trade, and D.H. Robertson contributed to the conceptual framework of Utility Terms of Trade. Matching these correctly yields the sequence a-4, b-3, c-2, d-1.

Taxes are categorized into direct and indirect. Death duty, wealth tax, and income tax are direct taxes, meaning the burden falls directly on the individual or entity. Excise duty is an indirect tax levied on the production or sale of goods, where the burden can be shifted to the consumer.

Total revenue is calculated by multiplying the quantity of goods sold by the price per unit. It represents the gross income generated by a business before any costs or expenses are deducted. It is a fundamental metric for assessing the scale of a firm's market activity and sales performance.

In economics and farm management, the total cost (TC) represents the sum of all expenses incurred during production. It is mathematically defined as the summation of total fixed costs (TFC), which do not change with output levels, and total variable costs (TVC), which fluctuate based on the quantity of production. Therefore, TC = TFC + TVC.