Which of the following observations is true? a. The ability to buy goods is divided equally among consumers. b. Free markets will achieve all of society's goals. c. The market system encourages firms to use inputs wastefully. d. The market leads to efficiency in production through the profit motive.

1. **Option (a):** The statement claims that the ability to buy goods is divided equally among consumers. However, in a market economy, income and wealth are generally distributed unevenly. Therefore, this statement is not true. 2. **Option (b):** The statement asserts that free markets will achieve all of society's goals. Free markets are efficient in allocating resources but do not automatically achieve every societal goal, such as equity, environmental protection, or social welfare. Hence, this statement is not true. 3. **Option (c):** The statement suggests that the market system encourages firms to use inputs wastefully. In reality, firms in a competitive market are motivated to reduce costs and maximize profits, which leads them to use inputs more efficiently. Thus, this observation is incorrect. 4. **Option (d):** The statement indicates that the market leads to efficiency in production through the profit motive. In a market system, firms are incentivized by profit to minimize production costs and innovate, which results in productive efficiency. This is a widely recognized positive attribute of market economies. Thus, the correct observation is: \( \boxed{d} \)