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Assuming ideal gas behaviour, what is the ratio of the density of ammonia (NH3) to the density of helium (He) at the same temperature and pressure?

1. 1.64
2. 0.42
3. 4.25
4. 5.4

Correct answer: 4.25

Solution

Density ratio = M(NH3) / M(He) = 17 / 4 = 4.25. At the same T and P, density is directly proportional to molar mass for ideal gases.

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