Calorimeter is a small container made of a thin sheet of _________ with good thermal conductivity.

Correct — D. A calorimeter vessel is made of copper, option (d), and two properties decide it.

High thermal conductivity — about 400 watts per metre per kelvin, so the vessel and its contents settle to one temperature quickly.
Low specific heat — about 385 joules per kilogram per kelvin, so the vessel itself absorbs very little of the heat you are trying to measure.

Copper is also cheap and malleable enough to roll into a thin sheet, which cuts its heat capacity further still.

Why the others are wrong

• (a)
  cesium — Cesium melts at about 28 degrees Celsius and reacts violently with water and air. It cannot be formed into a vessel at all, let alone one meant to hold warm liquids.
• (b)
  platinum — Platinum conducts heat far worse than copper, at roughly 70 watts per metre per kelvin, and costs a fortune. Its laboratory use is in resistance thermometers and electrodes, not calorimeter vessels.
• (c)
  silver — Silver does conduct heat slightly better than copper, but its price rules it out of routine laboratory equipment. Copper delivers nearly the same conductivity for a tiny fraction of the cost.

Calorimetry measures heat through the law of mixtures: heat lost by the hotter body equals heat gained by the colder one, once both reach a common temperature.

For that equation to hold, the container must interfere as little as it can. Hence the standard design — a thin copper vessel with a copper stirrer, standing on an insulating pad inside an outer jacket, with a lid and a thermometer through it.

A metal that conducts fast and stores little makes the vessel a quick, nearly invisible participant in the exchange.

Key facts

• A calorimeter is a thin copper vessel with a copper stirrer, held inside an insulating jacket.
• Copper's thermal conductivity is about 400 watts per metre per kelvin.
• Copper's specific heat capacity is about 385 joules per kilogram per kelvin, far below water's 4,186.
• The principle of calorimetry is the law of mixtures, where heat lost equals heat gained.

Common traps

• Picking silver because it is the best thermal conductor, without weighing cost and practicality.
• Reasoning that a good conductor would let heat escape, when the vessel is insulated outside and needs to equalise fast inside.

No directly related past PYQ was found.