Option 1: Constant -> In cardinal utility analysis, this is the fundamental assumption that marginal utility of money remains constant.
Option 2: Decreasing -> This is not assumed in cardinal utility analysis; it applies to individual commodities, not money.
Option 3: Increasing -> This contradicts the basic assumption of cardinal utility theory.
Option 4: First decreasing and then increasing -> This pattern is not considered in cardinal utility analysis.
Hence, Option 1: Constant -> In cardinal utility analysis (Marshallian approach), one of the key assumptions is that the marginal utility of money remains constant. This assumption is made to use money as a measuring rod of utility, allowing utility to be measured in cardinal terms (absolute numbers). While the law of diminishing marginal utility applies to individual commodities, money itself is assumed to have constant marginal utility to simplify the analysis and make utility measurable in monetary units. -> correct