121. Which command validates collection documents?

• a) db.collection.validate()
• b) db.checkDocuments()
• c) mongod --validate
• d) db.validateAll()

122. What is the purpose of the $dayOfMonth operator?

• a) Returns day number (1-31)
• b) Calculates month duration
• c) Groups by calendar days
• d) Validates date formats

123. Which method creates a MongoDB Atlas Data Lake?

• a) Atlas UI/API only
• b) db.createDataLake()
• c) mongod --dataLake
• d) db.makeDataLake()

124. What does the $cond operator do?

• a) Implements if-then-else logic
• b) Checks document condition
• c) Validates queries
• d) Tests server health

125. Which operator performs set union?

• a) $setUnion
• b) $union
• c) $mergeArrays
• d) $concat

126. What is the purpose of the $last operator in $group?

• a) Returns last document's value per group
• b) Gets final array element
• c) Identifies most recent timestamp
• d) Marks end of pipeline

127. Which command enables MongoDB's free monitoring?

• a) db.enableFreeMonitoring()
• b) mongod --enableMonitoring
• c) db.monitoring.start()
• d) db.freeMonitoring.enable()

128. What does the $rtrim operator do?

• a) Removes whitespace from string end
• b) Trims arrays from right
• c) Right-aligns text
• d) Reduces document size

129. Which method returns MongoDB's host info?

• a) db.hostInfo()
• b) db.serverHost()
• c) mongod --hostinfo
• d) db.status().host

130. What is the purpose of the $dateToParts operator?

• a) Decomposes date into components
• b) Converts parts to full date
• c) Validates date segments
• d) Formats date strings

131. Which operator checks if arrays are subsets?

• a) $setIsSubset
• b) $isSubset
• c) $containsAll
• d) $subset

132. What does the $avg operator do in $group?

• a) Calculates arithmetic mean
• b) Returns median value
• c) Computes moving average
• d) Validates number ranges

133. Which command lists all MongoDB features?

• a) db.features()
• b) show features
• c) db.listFeatures()
• d) No direct command (use docs)

134. What is the purpose of the $objectToArray operator?

• a) Converts object to key-value pairs array
• b) Validates object structure
• c) Creates arrays from nested objects
• d) Flattens documents

135. Which operator checks if arrays share elements?

• a) $setIntersection
• b) $anyElementTrue
• c) $setEquals
• d) $allElementsTrue

136. What does the $stdDevPop operator return?

• a) Population standard deviation
• b) Sample standard deviation
• c) Statistical variance
• d) Probability distribution

137. Which method returns MongoDB's network stats?

• a) db.serverStatus().network
• b) db.networkStats()
• c) mongod --network
• d) db.connectionInfo()

138. What is the purpose of the $arrayToObject operator?

• a) Converts key-value array to object
• b) Validates array structure
• c) Creates nested objects
• d) Maps arrays to documents

139. Which operator checks if arrays are disjoint?

• a) $setDisjoint
• b) $noCommon
• c) $unique
• d) $separate

140. What does the $trim operator do?

• a) Removes whitespace from both ends
• b) Shortens arrays
• c) Compacts documents
• d) Cleans invalid chars