Which property of air determines whether a cloud droplet is liquid water or ice?

As the warm air rises, it cools. When the warm air cools, some of the water vapor condenses. That means the water vapor changes phase into liquid water droplets. If the air is very cold, water vapor might change phase into ice crystals.

I'm not 100% sure if this is correct. My lesson question had said "What determines whether water vapor in the atmosphere becomes liquid water droplets or ice crystals?"

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