Pressure units: 1 torr is equal to how many millimetres of mercury (mm Hg)?

Introduction / Context:
Pressure units arise across vacuum systems, distillation columns, and laboratory measurements. Torr and mm Hg are closely related historical units, and recognizing their equivalence avoids confusion during unit conversions.

Given Data / Assumptions:

• Definition: 1 torr was historically defined as exactly 1 mm Hg.
• Modern standards set 1 torr = 133.322 Pa and 1 mm Hg (at 0 °C) ≈ 133.322 Pa, preserving practical equivalence.

Concept / Approach:
Because both units trace to the same physical mercury column height at standard gravity and temperature, they are effectively identical for routine engineering use, though Pascal is preferred in SI contexts.

Step-by-Step Solution:

Verification / Alternative check:
Check with standard conversions: 760 mm Hg = 760 torr ≈ 101325 Pa (1 atm), confirming equivalence.

Why Other Options Are Wrong:

• 0.1 or 10 or 1000 mm Hg would imply inconsistent scaling with atmospheric pressure and are not supported by definitions.

Common Pitfalls:
Confusing “torr” with “mTorr” (millitorr); remember 1 mTorr = 0.001 torr = 0.001 mm Hg.

Final Answer:
1