Which of the following gases behaves most like an ideal gas under standard conditions?

• A. H_2O
• B. He
• C. NH_3
• D. CO_2

Answer: (B)

Verified step by step guidance

1. Recall that an ideal gas is a hypothetical gas whose particles do not interact and occupy no volume. Real gases behave more like ideal gases at low pressure and high temperature, where intermolecular forces and molecular volume are negligible.
2. Consider the molecular properties of each gas: He (helium) is a noble gas with very small, nonpolar atoms and minimal intermolecular forces; H_2O (water vapor) is polar and forms hydrogen bonds; NH_3 (ammonia) is polar and also exhibits hydrogen bonding; CO_2 (carbon dioxide) is linear and nonpolar but has stronger intermolecular forces than helium due to its larger size.
3. Since ideal gas behavior improves with smaller, nonpolar molecules and weaker intermolecular forces, helium (He) is expected to behave most like an ideal gas under standard conditions.
4. Compare the gases by their molecular complexity and polarity: He is monatomic and nonpolar, while the others are polyatomic and have stronger intermolecular attractions, which cause deviations from ideal gas behavior.
5. Therefore, the gas that behaves most like an ideal gas under standard conditions is helium (He).