Which of the following is not a popular file extension of an audio file?

Correct option is B

.mp3, .wav and .flac are established audio file formats: MP3 is lossy and ubiquitous; WAV is uncompressed/PCM (or container for PCM); FLAC is lossless compression. Conversely, .pdf stands for Portable Document Format, designed for documents—text, vector graphics, images—not audio playback. While a PDF can embed multimedia, the file itself is not an audio format and requires a viewer to handle any embedded media. Therefore, among the given options, .pdf is not a popular audio file extension. The others are commonly used in music, voice recordings, and professional audio workflows.
Important Key Points
1. MP3: Lossy compression; excellent for streaming and portable devices due to small size.
2. WAV: Typically uncompressed PCM; high fidelity; common in recording, editing, and archival.
3. FLAC: Lossless compression; smaller than WAV with no quality loss; favored by audiophiles.
4. PDF: Document format for fixed-layout pages; supports text, images, and forms— not an audio format.
5. Compatibility: MP3/WAV/FLAC supported by most media players; PDFs need a PDF reader.
6. Use cases: MP3 (distribution), WAV (production), FLAC (archival/playback with full fidelity).
Knowledge Booster
· Why not (a) mp3 / (c) wav / (d) flac? All three are standard audio formats recognized by OS media frameworks and DAWs.
· Embedded media in PDFs: Some PDFs may include audio/video, but playback depends on the viewer and security settings; the file type remains a document.
· Other audio extensions: AAC/M4A, OGG/Opus, AIFF, ALAC are also common in various ecosystems.