UPSC CSE Prelims

Correct Option: C (1, 3 and 4 on1y) Explanation: Visible-light communication (VLC) transmits data using the visible portion of the electromagnetic spectrum and can achieve high data rates without radio-frequency interference; it is ordinarily short-range/line-of-sight. Statement / Pair / Item-wise Analysis: 1. Correct - Visible wavelengths are approximately 375–780 nanometres (definition varies slightly). 2. Incorrect - VLC is generally short-range optical wireless communication, not inherently long-range. 3. Correct - High-bandwidth VLC implementations can exceed typical Bluetooth data rates. 4. Correct - VLC does not emit radio-frequency electromagnetic interference, although ambient light can cause optical interference. Option-wise Analysis: A. Incorrect-includes incorrect item 2 (VLC is generally short-range optical wireless communication, not inherently long-range); omits correct item 4 (VLC does not emit radio-frequency electromagnetic interference, although ambient light can cause optical interference). B. Incorrect-includes incorrect item 2 (VLC is generally short-range optical wireless communication, not inherently long-range); omits correct item 3 (High-bandwidth VLC implementations can exceed typical Bluetooth data rates). C. Correct-includes all and only valid statements/items 1, 3, 4. D. Incorrect-includes incorrect item 2 (VLC is generally short-range optical wireless communication, not inherently long-range); omits correct item 1 (Visible wavelengths are approximately 375–780 nanometres (definition varies slightly)). Review note: Statement 4 means no RF interference, not complete immunity from all electromagnetic/optical interference.