The correct option is No upper limit.

No upper limit is correct because Azure Cosmos DB does not impose a fixed maximum number of databases per account. You can create as many databases as your application requires and practical constraints are driven by provisioned throughput, storage usage, and other account resource quotas rather than a hard count limit.

50 databases is incorrect because Cosmos DB does not restrict accounts to exactly fifty databases and that number is not a documented hard limit.

250 databases is incorrect because there is no published fixed cap at two hundred and fifty databases per account and the service scales based on resource and throughput considerations.

1 database is incorrect because an Azure Cosmos account can host multiple databases and it is not limited to a single database.

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