How can salt harden melting ice and also melt ice?

Question

I did the experiment using the string, salt, and ice. The ice did attach to the string, showing that the ice re-froze. But salt also melt ice, how can the ice re-froze in the experiment?

Answer 1

Salt lowers the melting temperature of ice.

This means that it causes the ice to freeze at a lower temperature.

It can also bring down the melting temperature causing it to melt at temperatures where it might otherwise stayed frozen.