Explanation:

Box 1: Yes
The ItemDescription field in not searchable.
Box 2: No
The ItemDescription field in not searchable, but we would need to recreate the index.
Box 3: Yes
An indexer in Azure Search is a crawler that extracts searchable data and metadata from an external Azure data source and populates an index based on field-to-field mappings between the index and your data source.
This approach is sometimes referred to as a 'pull model' because the service pulls data in without you having to write any code that adds data to an index.
Box 4: No
References:
https://docs.microsoft.com/en-us/azure/search/search-what-is-an-index
https://docs.microsoft.com/en-us/azure/search/search-indexer-overview