Among the examples given (Grape, Apple, Olive, Orange), the word "Olive" is likely to take most people the longest to identify as a fruit.
The reason for this is that olives are not commonly perceived as fruits in everyday language and culinary contexts. While olives are technically classified as fruits botanically, they are typically associated more with savory foods, such as being used as a topping or ingredient in salads, pizzas, and Mediterranean cuisine.
On the other hand, grapes, apples, and oranges are widely recognized and commonly referred to as fruits in various culinary contexts and everyday conversations. Grapes are well-known as small, round fruits often eaten as snacks or used in the production of wine. Apples are familiar as round, often red or green fruits consumed fresh or used in cooking and baking. Oranges are recognized as citrus fruits with a characteristic orange color and a sweet-tangy taste.
Due to the less common association of olives with the concept of fruits in everyday language and culinary usage, it may take people slightly longer to identify "Olive" as a fruit compared to the other examples given.