why is 0 degress celsius considered both the freezing point of water and melting point of ice?

Answer 1

Zero degrees Celsius is the exact temperature that water begins to freeze and ice begins to melt. Temperatures above 0 will cause ice to melt and below 0 will cause water to freeze.

Answer 2

So then the question becomes:

At 0 degrees Celsius, is water a solid or liquid?

Answer 3

Yes.

Maybe it's slush.

Answer 4

Ms Sue is right. A mixture of ice and water will have a temperature of zero Celsius. If heat is added all of it will melt but the temperature will not rise above zero C until the last bit of ice has melted. If heat is extracted all of it will freeze but the temperature of the mixture will not dip below zero C until the last bit of liquid water has frozen.