The supported mongosh helpers for replica-set membership changes are rs.remove() and rs.add(). rs.remove(hostname) removes the member whose host string matches the supplied host:port, while rs.add() adds a new member using either a host string or a member configuration document that includes a host field. Option C uses those documented methods in the required sequence: remove node 1, remove node 2, then add node 1 back. The names rs.removeNode() and rs.addNode() shown in the other options are not standard MongoDB replica-set helper methods. Membership changes must be performed carefully because modifying voting or data-bearing membership can affect majority calculations, elections, and availability. Administrators normally execute membership changes while connected to the current primary, allow configuration propagation, and verify replica-set health afterward with rs.status() or related diagnostics. If a removed data-bearing node is later re-added, it may need to synchronize depending on how far its data has diverged from the current replica-set history. Among the choices, option C is the only valid command sequence.

Study Guide reference/topic:Cluster Reliability and Data Resilience - replica-set membership, rs.remove(), rs.add(), and topology changes.

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logLevel is a MongoDB server parameter, and server parameters are retrieved through the administrative getParameter database command. The documented and unambiguous mongosh form is db.adminCommand({ getParameter: 1, logLevel: 1 }), which executes the command against the admin database and requests the current value of logLevel. The first numeric value activates the command, while the logLevel field identifies the parameter to return. Options B and C refer to a db.getParameter() helper that is not the documented interface. Option A uses db.runCommand() without explicitly switching to the admin database. Because getParameter is an administrative command, db.adminCommand() is the correct and reliable form among the choices. Administrators use server parameters to inspect and, where supported, tune aspects of mongod or mongos behavior. logLevel controls global diagnostic verbosity, while component-specific verbosity can be managed through the logging configuration. For this question, option D precisely matches the expected administrative syntax. Checking the current value before changing logging settings is also a sound operational practice during troubleshooting.

Study Guide reference/topic:Performance Monitoring and Tuning - runtime server parameters, logging configuration, and getParameter.

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MongoDB provides db.grantRolesToUser() specifically for assigning one or more additional roles to an existing user. The method takes the username as its first argument and an array of roles as its second argument, so db.grantRolesToUser( " user1 " , [ " customRole1 " ]) is the correct choice. A role can be supplied as a simple string when it belongs to the current database or as an explicit document such as { role: " customRole1 " , db: " admin " } when the database context must be specified. Option B uses db.createUser(), which is used to create a new user rather than modify the role membership of an account that already exists. Options A and C use method names that are not the documented mongosh interfaces for this operation. Administrators should also distinguish grantRolesToUser() from grantRolesToRole(): the latter makes a user-defined role inherit other roles, whereas the former directly changes a user ' s assigned roles. Least-privilege practice requires granting only roles necessary for the user ' s responsibilities. For the requested update to the existing user, option D is correct.

Study Guide reference/topic:Security, Networking, and Encryption - user administration, role assignment, RBAC, and grantRolesToUser().

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MongoDB stores records as BSON documents. BSON, short for Binary JSON, is a binary serialization format that preserves the JSON-like document model while supporting a richer set of data types required by database applications. Mongosh commonly displays documents using JavaScript or Extended JSON-like notation, which is why JSON is a tempting distractor, but the native stored representation is BSON. BSON supports types such as ObjectId, dates, binary data, timestamps, Decimal128, 32-bit and 64-bit integers, arrays, embedded documents, and other values that standard JSON does not represent natively. Base64 is an encoding technique often used to render binary data as text and is not MongoDB ' s document storage format. XML is also unrelated to MongoDB ' s native representation. Understanding BSON is fundamental for database administrators because document-size limits, type comparisons, index keys, serialization behavior, and driver interoperability all depend on BSON semantics. The flexible document model allows fields to contain scalar values, nested documents, and arrays within the same record structure. Therefore the encoded format used by MongoDB to store documents is BSON, making option C correct.

Study Guide reference/topic:MongoDB Architecture and Core Operations - BSON, document structure, data types, and JSON/BSON distinctions.

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updateMany() distinguishes between documents that match the filter and documents whose stored data actually changes. The filter { diagnosis: " Hypertension " } matches Carlos Martinez and Maria Lopez, so matchedCount is 2. Carlos currently has room: 203, and $set: { room: 207 } changes his document, contributing one to modifiedCount. Maria already has room: 207. She still satisfies the filter and therefore counts as a match, but setting a field to the value it already contains does not produce a material modification, so she does not increment modifiedCount. Juan Perez has diagnosis Arrhythmia, so he is neither matched nor modified. The resulting acknowledged operation therefore reports matchedCount: 2 and modifiedCount: 1, corresponding to option D. This distinction is essential when validating whether an update actually changed stored values rather than merely identifying matching records. This distinction is operationally important: a large difference between matched and modified counts can indicate that many matching documents already contained the requested state, not that the update failed. DBAs should use both counters when validating bulk-update behavior.

Study Guide reference/topic:MongoDB Architecture and Core Operations - updateMany(), $set, matchedCount, and modifiedCount.

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The grantPrivilegesToRole command requires privileges to be an array of privilege documents. Each privilege document must contain a resource document and an actions array. Option A uses exactly that structure: the resource targets testDB with an empty collection name, which represents the database-level collection scope used by MongoDB ' s privilege model, and the actions list contains " find " . Option B omits the required resource wrapper and incorrectly places db and collection directly in the privilege document. Option C supplies privileges as a single document rather than as the required array. Option D has the correct resource structure but supplies actions as a scalar string instead of an array. The find action grants the ability to perform supported read operations on the specified resource scope, subject to the role ' s other inherited privileges. The shown writeConcern and comment fields are legitimate command options and do not change the structural requirement. Consequently, option A is the only choice that conforms to MongoDB ' s documented privilege document format.

Study Guide reference/topic:Security, Networking, and Encryption - user-defined roles, privilege documents, resources, actions, and grantPrivilegesToRole.

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