UPSC Prelims 2020— Question 19

This question tests visible light communication. The key concept is: Visible Light Communication uses visible-spectrum light, especially LEDs, to transmit data. It can provide high data rates and is immune to radio-frequency electromagnetic interference, but it is not inherently a long-range technology. The correct combination therefore includes 1, 3 and 4. The verified answer for the uploaded Set-B paper is option C. Option A — 1, 2 and 3 only: This is not the correct option. The option does not match the verified combination or conclusion. The decisive point is the distinction explained above: Visible Light Communication uses visible-spectrum light, especially LEDs, to transmit data. It can provide high data rates and is immune to radio-frequency electromagnetic interference, but it is not inherently a long-range technology. The correct combination therefore includes 1, 3 and 4. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. Option B — 1, 2 and 4 only: This is not the correct option. The option does not match the verified combination or conclusion. The decisive point is the distinction explained above: Visible Light Communication uses visible-spectrum light, especially LEDs, to transmit data. It can provide high data rates and is immune to radio-frequency electromagnetic interference, but it is not inherently a long-range technology. The correct combination therefore includes 1, 3 and 4. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. Option C — 1, 3 and 4 only: This is the correct option. It matches the verified conclusion because Visible Light Communication uses visible-spectrum light, especially LEDs, to transmit data. It can provide high data rates and is immune to radio-frequency electromagnetic interference, but it is not inherently a long-range technology. The correct combination therefore includes 1, 3 and 4. The wording of the option is consistent with the governing concept tested by the question. Option D — 2, 3 and 4 only: This is not the correct option. The option does not match the verified combination or conclusion. The decisive point is the distinction explained above: Visible Light Communication uses visible-spectrum light, especially LEDs, to transmit data. It can provide high data rates and is immune to radio-frequency electromagnetic interference, but it is not inherently a long-range technology. The correct combination therefore includes 1, 3 and 4. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. For UPSC-style elimination, first identify the exact proposition being tested, then evaluate each statement independently before comparing the answer codes. Avoid treating a broad or absolute statement as correct merely because its general theme is familiar. The precise qualifiers in the question—such as 'all', 'only', 'cannot', 'largest', 'always' or a specific institutional role—often determine the answer. On that basis, option C is the verified answer.