Correct Answer: Cardinal units

Solution : The correct answer is (d) Cardinal units.

The cardinal theory of consumer's equilibrium assumes that utility can be measured and quantified numerically. It suggests that consumers can assign cardinal (numerical) values to the satisfaction or utility they derive from consuming goods and services. This allows for the comparison of utility across different goods and the determination of consumer equilibrium based on maximizing total utility or marginal utility.

In contrast, the ordinal theory of consumer's equilibrium (opposite to cardinal theory) only considers the ranking or ordering of preferences without assigning specific numerical values to utility.