All of the following are keratinised EXCEPT:

The crevicular epithelium is not keratinized, making it the correct answer in this context. This specific type of epithelium lines the gingival sulcus, the space between the teeth and the surrounding gum. It is characterized by being non-keratinized, which allows for a better response to inflammation and facilitates its role in oral health, particularly in the presence of dental plaque.

In contrast, palatal epithelium, attached gingiva, and alveolar mucosa feature keratinized areas. The palatal epithelium is typically keratinized due to the region’s exposure to the oral cavity's harsh environment, helping protect underlying tissues. Similarly, attached gingiva is keratinized to provide durability and support against mechanical forces during functions like chewing. Finally, while alveolar mucosa may contain keratin and is protective, it is more often classified based on the presence of non-keratinized tissues, similar to crevicular epithelium.

In summary, acknowledging the role of different types of epithelial tissues in the oral cavity helps clarify why crevicular epithelium stands out as non-keratinized in this instance.