Universal gas constant R: Choose the correct value in kcal per kg-mol per °C (practical engineering units).

Introduction / Context:
The universal gas constant R appears in equations of state (e.g., PV = nRT) and energy relations. Engineers often use convenient unit systems; one common choice is kcal per kg-mol per K (or °C for incremental differences).

Given Data / Assumptions:

• Reference values: R = 8.314 kJ/mol·K = 1.987 kcal/mol·K.
• In many chemical engineering texts, “kg-mol” is used synonymously with “kmol” and retains the same numerical constant when paired consistently with other units.

Concept / Approach:
Unit conversions: 1 kcal = 4.184 kJ. Therefore 8.314 kJ/mol·K ÷ 4.184 ≈ 1.987 kcal/mol·K. In engineering usage this is frequently written per kg-mol·K with the same numerical value when moles are the basis entity in the chosen unit system.

Step-by-Step Solution:

Verification / Alternative check:
Cross-check with English units: R ≈ 1.987 Btu/lb-mol·°R, consistent numerically, confirming the conversion pattern.

Why Other Options Are Wrong:

• 2.79 and 3.99 are not equal to R in these units.
• “None of these” is incorrect because 1.987 is correct and widely used.

Common Pitfalls:
Mixing per mol and per kmol without adjusting other units; always keep unit systems internally consistent.

Final Answer:
1.987