According to the Theory of Consumer Behaviour, Inequality $p_1x_1 + p_2x_2≤M$ is called the Consumer's _____.

Budget Constraint

The correct answer is Option (2) → Budget Constraint

According to the Theory of Consumer Behaviour, Inequality $p_1x_1 + p_2x_2≤M$ is called the Consumer's  Budget Constraint.

Suppose the income of the consumer is M and the prices of bananas and mangoes are $p_1$  and $p_2$ respectively . If the consumer wants to buy $x_1$ quantities of bananas, she will have to spend $p_1x_1$ amount of money. Similarly, if the consumer wants to buy $x_2$ quantities of mangoes, she will have to spend $p_2x_2$ amount of money. Therefore, if the consumer wants to buy the bundle consisting of $x_1$ quantities of bananas and $x_2$ quantities of mangoes, she will have to spend $p_1x_1 + p_2x_2$ amount of money. She can buy this bundle only if she has at least $p_1x_1 + p_2x_2$ amount of money. Given the prices of the goods and the income of a consumer, she can choose any bundle as long as it costs less than or equal to the income she has. In other words, the consumer can buy any bundle ($x_1$ , $x_2$ ) such that

$p_1x_1 + p_2x_2≤M$

The inequality as given above is called the consumer’s budget constraint. It refers to the limitation imposed on a consumer's choices due to their limited budget and the prices of goods they want to buy. The inequality (p₁x₁ + p₂x₂ ≤ M) mathematically represents this constraint.

Consumer's Budget: This refers to the total amount of money a consumer has available to spend.

Budget set: The set of bundles available to the consumer is called the budget set. The budget set is thus the collection of all bundles that the consumer can buy with her income at the prevailing market prices. The budget constraint defines the boundary of this set.

The term "budget behaviour" is not a standard term in the Theory of Consumer Behaviour.