[mohd]

Why does water has negative slop on the phase diagram ? what does this say about the properties of liquid and solid water ??

thanks

[tamim83]

Hi,
Please read the forum rules.  You have to show us you made an effort to answer the question yourself.  You have asked 3 questions without showing this effort. 

Now to your question: solid water (ice) is less dense than liquid water.  For most substances, the opposite is true.  So increasing the pressure of the system causes the melting point to increase.  Since ice is less dense than liquid water, increasing the pressure actually causes the melting temperature to decrease, resulting in the negative slope of the  solid-liquid boundary line in the phase diagram.