The main aim of consumer is to get maximum satisfaction. So he/she should try consume more and more of oranges till its marginal utility is positive.
At zero point of level the consumer should stop consumption.

When to Buy More Oranges?
• Diminishing Marginal Utility: The principle of diminishing marginal utility states that as a consumer consumes more of a good, the satisfaction or utility derived from each additional unit decreases.
• Optimal Consumption: To determine when a consumer should buy more oranges, they should consider the marginal utility derived from each additional orange compared to the price of the orange.
• Equilibrium Point: The consumer should continue to buy more oranges until the marginal utility of the orange is equal to the price of the orange. At this point, the consumer is maximizing their utility.
• Price Changes: If the price of oranges decreases, the consumer may be willing to buy more as the marginal utility now exceeds the price. Conversely, if the price increases, the consumer may choose to buy fewer oranges.
• Consumer Preferences: It is important for the consumer to consider their own preferences and budget constraints when deciding how many oranges to buy. Factors such as taste, health benefits, and overall satisfaction should be taken into account.
• Timing: The consumer should also consider the timing of their purchase. For example, buying oranges in bulk when they are in season and prices are lower can be a cost-effective strategy.
In conclusion, a consumer should buy more oranges when the marginal utility of the orange is greater than or equal to the price, taking into account individual preferences and budget constraints. By understanding the principle of diminishing marginal utility, consumers can make informed decisions about their purchases.