Charles's law predicts that a gas cooled at constant pressure would reach zero volume at

Explanation

Extrapolating the straight line of volume against temperature backwards, every gas reaches zero volume at minus 273.15 degrees Celsius, which is defined as absolute zero or 0 K. The extrapolation is theoretical, since every real gas liquefies well before that point. This is precisely why the Kelvin scale exists and why gas law calculations must use it.