If a server cannot fulfill a request due to bad syntax, which HTTP status code class is most appropriate?

• A. 1xx Informational
• B. 2xx Successful
• C. 3xx Redirection
• D. 4xx Client Error

Answer: (D)

Bad syntax in a request means the client sent something the server can’t even parse, so the problem is with what the client sent rather than with the server’s processing. That’s why the 4xx range is used—these codes indicate a client error. The server is telling the client to fix the request before trying again. A typical representative code is 400 Bad Request, which explicitly signals malformed syntax. The other classes don’t fit: 1xx are informational, not errors; 2xx means the request was successfully processed; 3xx indicates the client should take additional action (like following a redirect) rather than reporting a syntax problem.