Option 1 -> Incorrect. The law states marginal utility decreases, not increases.
Option 2 -> Incorrect. Marginal utility does not remain constant as consumption increases.
Option 3 -> Correct. This accurately describes the law's principle.
Option 4 -> Incorrect. While marginal utility may reach zero eventually, the law states it 'begins to decrease', not necessarily becomes zero.
Hence, Option 3: begins to decrease -> The Law of Diminishing Marginal Utility is a fundamental economic principle stating that as a consumer consumes additional units of a commodity in succession, the marginal utility (additional satisfaction) derived from each successive unit begins to decrease. For example, the first slice of pizza provides high satisfaction, the second provides less, and by the fifth or sixth slice, the additional satisfaction diminishes significantly. This happens because the consumer's want for that commodity gets progressively satisfied with each unit consumed. -> correct