Why does sound travel slightly faster through humid air than through dry air, at the same temperature?

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1. Why does sound travel slightly faster through humid air than through dry air, at the same temperature?

Water vapour is denser than dry air, adding more inertia

Water vapour is less dense than the dry air it displaces, lowering the air’s overall density

Humidity increases the air’s pressure, which speeds up sound

Humidity has no genuine effect on the speed of sound

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Water vapour molecules are lighter than the nitrogen and oxygen molecules they displace, so humid air is slightly less dense than dry air. Lower density allows sound to travel a little faster.