Which of the following is a key property of fiat currency?

Fiat currency is money that derives its value primarily from government decree and public confidence rather than from being directly convertible into a commodity such as gold. A key property is that it is declared legal tender, meaning it must be accepted for payment of debts within the jurisdiction and is recognised by the state for settling transactions and paying taxes. This legal tender status supports general acceptability and underpins the monetary system. The other options are not defining characteristics. Devaluation can happen to any currency under certain conditions and is not specific to fiat systems. Operating in an exchange rate mechanism describes a policy arrangement between currencies, not a property of fiat currency itself. Being pegged to the US dollar is a specific exchange rate policy that some countries adopt, but many fiat currencies float freely or use other regimes. The examinable concept is that fiat money is not backed by intrinsic commodity value and is sustained by legal framework, monetary policy credibility, and trust. Therefore, being declared legal tender is the correct key property.