What is the main job of Bitcoin miners?
Correct answer
Answer B: They group transactions together and use computing power to find a valid block.
Quick explanation
It can be compared with an enormous number of dice rolls: miners continually try different values and calculate hashes. Whoever first finds a valid block hash can propose the next block.
Detailed explanation
Bitcoin miners build a candidate block from available transactions. It includes a coinbase transaction through which a successful miner can claim the permitted block subsidy and included transaction fees. Miners then change fields in the block header and calculate huge numbers of hashes. They seek a header hash below the current target.
If a miner finds suitable proof of work, it broadcasts the block. That does not automatically make the block valid. Full nodes independently check that all transactions, signatures, amounts, spending conditions and proof of work comply with their consensus rules. An invalid block is discarded even if creating it required substantial computation.
Miners therefore have an important but limited role: they arrange transactions in candidate blocks, provide proof of work and propose new blocks. They do not hold every user's keys and cannot single-handedly replace the rules enforced by verifying nodes.
Example or everyday application
A mining pool finds a header hash below the target and sends its block. If it contains an excessive subsidy, full nodes reject it despite the work performed.
Common misconception
Beginners often equate mining with central bookkeeping. The explanation separates block creation, proof of work and independent validation.
Sources used
Bitcoin Developer Guide - Mining
This source is mainly intended for developers. The relevant information may therefore be harder to find.
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