Final answer:
Trade barriers decrease the average income in an economy by disrupting market efficiencies and specialization gained through comparative advantage. Governments may impose trade barriers to protect domestic industries or jobs, but this often leads to lower economic welfare. So, the correct answer is option b.
Step-by-step explanation:
Trade barriers typically decrease the average income level in an economy. When an economy is open to trade, firms and workers can specialize according to their comparative advantage, which increases the amount that the economy can produce. This specialization makes workers more productive and valuable, leading to higher wages as the demand for their labor increases. Therefore, the average level of wages in an economy tends to rise. However, when trade barriers are implemented, they can disrupt these efficiencies and reduce the overall level of wages in the economy.
Despite the negative impact on the average worker's income, governments might instate trade barriers for various reasons. These can include protecting nascent industries, preserving national security, safeguarding jobs in certain sectors, or responding to unfair trade practices by other countries. While they can protect certain industries or workers in the short term, they generally result in an overall reduction of economic welfare and average wages.
So, the correct answer is option b.