200-901 Understanding and Using APIs Practice Question
A developer is testing a custom REST API that returns a JSON error object with an HTTP 400 status when an invalid query parameter is sent. They want to confirm that the API is behaving correctly according to REST conventions. Which HTTP status code class indicates that the client's request contains an error that the client can potentially fix?
⚠ Common exam trap
The trap here is assuming that any error status indicates a server problem, which would lead to choosing the 5xx class instead of the correct 4xx class for an HTTP 400 response.
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
✓
4xx
HTTP status codes are grouped into classes, and the 4xx class is reserved for client errors. An HTTP 400 Bad Request is a 4xx code, so it signals that the client sent something invalid, such as a malformed query parameter. Recognizing this class helps developers distinguish between problems they can fix in their request and problems that originate on the server.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
5xx
Why it's wrong here
The 5xx class indicates server errors, meaning the server failed to fulfill an apparently valid request. In this scenario, the API returns 400, which is a client error, not a server error. Mistaking 5xx for the correct class would lead a developer to investigate server-side issues rather than correcting the client's request, wasting troubleshooting effort.
- ✓
4xx
Why this is correct
The 4xx class of status codes is specifically defined for client errors, indicating that the request contains bad syntax or cannot be fulfilled due to something the client did. An HTTP 400 (Bad Request) is a classic 4xx code, so this class correctly identifies that the client can potentially fix the request, for example by correcting the invalid query parameter.
- ✗
2xx
Why it's wrong here
The 2xx class indicates success, meaning the request was received, understood, and accepted. In this scenario, the API returns 400, which is not a success code. Confusing 2xx with client errors would lead a developer to incorrectly treat a failed request as successful, potentially causing the application to proceed with invalid data or skip necessary error handling.
- ✗
3xx
Why it's wrong here
The 3xx class indicates redirection, meaning further action needs to be taken by the client to complete the request. This is unrelated to an error such as HTTP 400. A developer who assumes 3xx covers client errors might implement redirect-following logic instead of validating input, which would not resolve the underlying problem of an invalid query parameter.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 200-901 practice question is part of Courseiva's free Cisco 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 200-901 exam.