Which of the following could suffer due to the deletion of an index?

The deletion of an index primarily impacts the performance of queries that rely on that index. An index in MongoDB acts as a data structure that improves the speed of data retrieval operations on a database. When an index is deleted, the database loses a mechanism to quickly access the relevant documents, leading to slower query performance, especially for large datasets.

Queries that previously benefited from the index may now require a full collection scan, which generally takes longer and is less efficient than accessing the data using an index. Thus, option B accurately reflects the consequence of removing an index, as the efficiency of query execution will decrease, and the response times for queries that depended on that index will suffer.

In contrast, while data integrity, schema design, and document structure are essential elements of a database, they are not directly affected by the presence or absence of an index. Data integrity refers to maintaining accuracy and consistency, which is not compromised merely by deleting an index. Similarly, schema design and document structure pertain to how data is organized and represented in the database, and these factors remain unchanged regardless of index deletion.