Which statement is true about pressure units?

• A. 1 psi equals 27.7 inches of water.
• B. 1 psi equals 2.2 inches of Mercury.
• C. 1 psi equals 0.5 inches of water.
• D. 1 psi equals 3.0 inches of Mercury.

Answer: (B)

When you compare pressure units, psi (pounds per square inch) is often related to other units like inches of mercury (inHg) and inches of water (inH2O). A standard way to relate them is through 1 atmosphere (1 atm) = 14.696 psi = 29.92 inches of mercury. From this, 1 psi ≈ 29.92 / 14.696 ≈ 2.04 inches of mercury. So the statement that 1 psi is about 2.0–2.04 inches of Mercury is the precise idea, and the option giving 2.2 inches of Mercury is the closest practical rounding used in many tables, making it the best match.

The other options aren’t as good: 1 psi equals about 0.5 inches of water is far off (it's closer to 27.7 inches of water), and 1 psi equals 3.0 inches of Mercury is noticeably higher than the true ~2.04 inches. The comparison to water is correct in its own right, but the question focuses on mercury, so the mercury-based statement that’s closest to the true value is chosen.