C100DEV MongoDB Overview and Document Model Practice Question
A developer is reviewing how MongoDB represents and stores data at the document level. Which TWO statements accurately describe the behavior of the BSON format and MongoDB documents? (Choose two.)
⚠ Common exam trap
The trap here is assuming BSON is just text JSON with extra types, when it is actually a binary format with its own type codes and a hard 16 MB document size limit.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The maximum size of a single BSON document in MongoDB is 16 MB, and this limit applies to the document as stored on the server.
BSON is a binary-encoded format that extends JSON with types such as ObjectId, Date, and Binary, each identified by a type code. MongoDB also enforces a 16 MB maximum document size, which affects how applications design their data model. These two facts are central to understanding how documents are represented and stored, and they explain why BSON is used rather than plain JSON.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Field order within a BSON document is not preserved, so queries that depend on field order will not work consistently.
Why it's wrong here
BSON preserves field order as written. The order is significant for some operations, such as when comparing documents for equality or when using the $natural sort on a capped collection. Saying field order is not preserved is incorrect; the server maintains the order in which fields appear in the document.
- ✗
BSON documents are stored as plain text JSON on disk to simplify backup and restore operations.
Why it's wrong here
BSON is a binary format, not plain text JSON. It is designed for efficient parsing, traversal, and storage. Tools like mongodump and mongorestore work with BSON, and the mongo shell or mongosh displays documents in a JSON-like format for readability, but the on-disk representation is binary. This statement mischaracterizes how MongoDB stores data.
- ✓
The maximum size of a single BSON document in MongoDB is 16 MB, and this limit applies to the document as stored on the server.
Why this is correct
MongoDB enforces a 16 MB limit on each BSON document. The limit is checked when documents are inserted or updated, and it applies to the stored document size. Applications that need to store larger payloads should use GridFS, which splits data across multiple documents. This limit is a fundamental constraint of the document model.
- ✓
BSON supports additional data types beyond JSON, such as ObjectId, Date, and Binary, which are stored as distinct type codes.
Why this is correct
BSON extends JSON with types such as ObjectId, Date, Binary, Decimal128, and Timestamp. Each value in a BSON document is prefixed by a type byte, so the server can distinguish these types without ambiguity. This is essential for MongoDB features like ObjectId generation and date queries, and it is a core reason BSON is used instead of plain JSON for storage.
- ✗
A MongoDB document can contain fields with duplicate names, and the server preserves both values when the document is stored.
Why it's wrong here
BSON does not support duplicate field names in a document. If a document is inserted with duplicate keys, the driver or server may reject it or the last value may overwrite earlier ones, depending on context. The server does not preserve both values, so this statement is incorrect and could lead to data loss if a developer relies on it.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DEV practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DEV exam.