Which of the following is an example of an **isolated** thermodynamic system?
AHot tea in an open cup placed on a table
BA reaction mixture in a sealed copper vessel
CBoiling water in a closed glass beaker
DHot coffee in a thermos flask sealed with its lid
Answer & Solution
Correct answer: D. Hot coffee in a thermos flask sealed with its lid
An isolated system permits neither matter nor energy exchange with the surroundings. A well-sealed thermos flask is designed precisely for this — vacuum jacket blocks heat transfer, the lid blocks matter exchange. The open cup is an open system (matter + energy). The sealed copper vessel is a closed system (no matter exchange, but copper conducts heat). The closed glass beaker is also closed (glass still conducts heat).
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