Pressure units equivalence:\nOne torr is, by definition, equal to which of the following pressure units under standard laboratory conventions?

Introduction / Context:
Pressure units appear in vacuum systems, distillation design, and physical measurements. Converting among units avoids errors in design calculations and instrument interpretation. The torr is widely used in vacuum technology and historically ties to the height of a mercury column.

Given Data / Assumptions:

• 1 torr is historically defined as 1 mm of mercury at standard gravity and temperature.
• Modern SI relations: 1 atm ≈ 760 torr ≈ 101325 Pa.

Concept / Approach:
By definition, 1 torr = 1 mm Hg (exact in many practical contexts; minor corrections exist for temperature/gravity and the adoption of the pascal). This clear mapping helps in quick mental conversions between vacuum gauge readings and SI units.

Step-by-Step Solution:

Verification / Alternative check:
Instrument manuals for vacuum gauges list torr and mm Hg interchangeably; conversion charts confirm the relation.

Why Other Options Are Wrong:

• 1 Pa: much smaller; 1 torr ≈ 133.322 Pa.
• 1 ata: equals 1 kgf/cm2; not equivalent to 1 torr.
• 1 mm wc: water column unit; ≈ 9.80665 Pa.
• 1 bar: 10^5 Pa; vastly larger than 1 torr.

Common Pitfalls:
Confusing torr with “Torricelli” in flow; remember torr is a pressure unit directly tied to mm Hg.

Final Answer:
1 mm Hg (millimetre of mercury).