Practice question

Heat lost by copper = Heat gained by water. mcsc(100−T) = mwsw(T−20). 0.5×386×(100−T) = 1×4186×(T−20). 19300−193T = 4186T−83720. 19300+83720 = 4186T+193T. 103020 = 4379T⇒T≈23.53∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 23.5°C. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.