What is a satoshi?
Correct answer
Answer A: The smallest unit: 100 million satoshis = 1 BTC.
Detailed explanation
A satoshi, often shortened to sat, is one hundred-millionth of a bitcoin. One BTC therefore equals 100,000,000 satoshis. On Bitcoin's base layer, amounts are represented as whole satoshi values.
Divisibility is not the same as additional money supply. Splitting a bitcoin into smaller units does not create more bitcoin, just as 100 cents is no more than one euro. The subunit simply allows very small values to be stated and transferred precisely.
The term is especially important because users do not need to own a whole bitcoin. Depending on settings, wallets can display balances in BTC or satoshis. Additional payment layers such as Lightning can use even smaller accounting units internally, but final settlement on the base layer uses whole satoshis. Finer subdivision therefore does not change the 21-million rule. It limits the number of bitcoin, while satoshis enable practical divisibility of that amount.
What the sources support
OpenStax explains divisibility as a useful property of money. Bitcoin sources define the satoshi as the smallest unit used by the protocol, applying the general monetary property of divisibility directly to Bitcoin.