In economics, a superior good (or normal good) is one for which demand increases as consumer income rises. Since household expenditure on motoring grows as income levels increase, it demonstrates a positive income elasticity of demand, classifying it as a superior good rather than an inferior good, which would see demand fall as income rises.

The substitution effect isolates the change in consumption resulting solely from the change in relative prices, holding the consumer's utility constant. Graphically, this is represented by a movement along the original indifference curve to a point where the slope matches the new price ratio. Movement from Z to X typically illustrates this adjustment in standard microeconomic models of consumer choice.

An inferior good is defined as a product for which demand decreases as consumer income rises. Therefore, an increase in income causes the demand curve for an inferior good to shift inward (to the left), reflecting a reduction in the quantity demanded at every price level.

The prediction that demand for a product will rise as consumer income rises is the defining characteristic of a normal good. Normal goods exhibit a positive income elasticity of demand. If chairs were inferior goods, demand would decrease as income rose. Therefore, the economist's model relies on the classification of chairs as normal goods.

An inferior good is defined by a negative income elasticity of demand, meaning consumption decreases as consumer income rises. Regarding price elasticity, the law of demand generally dictates that price elasticity is negative for most goods, including inferior goods, because quantity demanded moves inversely to price. While the provided answer A is standard, note that price elasticity is technically a separate concept from income elasticity.

When the wage rate rises, two opposing forces occur. The substitution effect makes leisure more expensive, encouraging more work. The income effect makes the individual wealthier, increasing the demand for leisure (a normal good) and reducing work. The net effect on labor supply depends on which force is stronger. If the substitution effect dominates, labor supply increases; if the income effect dominates, labor supply decreases.

Income elasticity measures how the quantity demanded of a good changes in response to a change in consumer income. Inferior goods have a negative income elasticity because demand falls as income rises. Conversely, luxury goods are highly sensitive to income changes, exhibiting an income elasticity greater than one, meaning the percentage increase in demand exceeds the percentage increase in income.

A movement along the demand curve is caused by a change in the price of the good. A shift in the supply curve changes the market equilibrium price, which subsequently causes a movement along the demand curve. Conversely, changes in income, the number of buyers, or advertising are 'shifters' that cause the entire demand curve to move.

The availability of close substitutes is a primary determinant of price elasticity of demand. When a good has few substitutes, consumers have little choice but to continue purchasing it even if the price increases, because they cannot easily switch to an alternative. This lack of alternatives makes the quantity demanded relatively unresponsive to price changes, resulting in a price inelastic demand curve.

The law of demand establishes an inverse relationship between the price of a good and the quantity demanded, holding all other factors constant. As the price rises, the opportunity cost of purchasing the good increases, leading consumers to reduce the quantity they are willing to buy.