UPSC Prelims 2020— Question 20

This question tests blockchain applications. The key concept is: A blockchain is a distributed ledger whose records are replicated and validated through a network rather than controlled by one central user. Blockchains are not limited to cryptocurrency; applications can include identity, supply chains and records. Open/public blockchain applications can be built without permission from a central authority, although permissioned systems also exist. The verified answer for the uploaded Set-B paper is option D. Option A — 1 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: A blockchain is a distributed ledger whose records are replicated and validated through a network rather than controlled by one central user. Blockchains are not limited to cryptocurrency; applications can include identity, supply chains and records. Open/public blockchain applications can be built without permission from a central authority, although permissioned systems also exist. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. Option B — 1 and 2 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: A blockchain is a distributed ledger whose records are replicated and validated through a network rather than controlled by one central user. Blockchains are not limited to cryptocurrency; applications can include identity, supply chains and records. Open/public blockchain applications can be built without permission from a central authority, although permissioned systems also exist. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. Option C — 2 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: A blockchain is a distributed ledger whose records are replicated and validated through a network rather than controlled by one central user. Blockchains are not limited to cryptocurrency; applications can include identity, supply chains and records. Open/public blockchain applications can be built without permission from a central authority, although permissioned systems also exist. Therefore this alternative should be eliminated even if part of its wording appears plausible in isolation. Option D — 1 and 3 only: This is the correct option. It matches the verified conclusion because A blockchain is a distributed ledger whose records are replicated and validated through a network rather than controlled by one central user. Blockchains are not limited to cryptocurrency; applications can include identity, supply chains and records. Open/public blockchain applications can be built without permission from a central authority, although permissioned systems also exist. The wording of the option is consistent with the governing concept tested by the question. 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 D is the verified answer.