Concept:The method of mixtures assumes no heat is lost to the surroundings or absorbed by the apparatus.
Explanation:The assumption “heat lost by the hot body equals heat gained by the cold body” requires that the system is perfectly insulated and that all heat exchanges are accounted for.
Lagging the calorimeter reduces heat loss to the environment, so condition I helps validate the assumption.
Using only S.I. units does not affect the energy balance, so condition II does not validate the assumption.
Weighing the calorimeter, lid, and stirrer allows their heat capacities to be included in the calculation, so heat absorbed by the apparatus is not ignored.
Therefore, condition III also helps validate the assumption.
Only I and III together satisfy the requirement.
Answer:C. I & III only