Thermometer offset error cancels in temperature differences

Steps:

• True ice point is 0°C, but thermometer reads 1°C, showing a +1°C offset.
• True boiling point is 100°C, but thermometer reads 101°C, confirming consistent +1°C offset.
• For initial water temperature T1°C (true), reading is T1 + 1°C.
• For final temperature T2°C (true), reading is T2 + 1°C; calculated rise is (T2 + 1) - (T1 + 1) = T2 - T1, matching true rise.

Why B is correct:

• Temperature differences are unaffected by uniform calibration offsets, per the principle that errors cancel in subtraction.

Why the others are wrong:

• A: Offset adds to both readings, so rise is not lowered.
• C: No net increase occurs, as offset is identical for both measurements.
• D: Double offset would imply inconsistent error, which is not the case.

Final answer: B