Under certain conditions the solid and liquid states of water can exist in equilibrium how are these conditions indicated on the phase diagram for water

in the phase diagram the line between solid and liquid is where both phases available at the same time

The phase diagram of water has following features

a) Triple point : this is the point of intersection of three curves and is the point where all the three phases of water exist together

The triple point of water is 273.16K, and 4.58 mm Hg

b) Curves : these represents the presence of two phases together

the curve is shared by any two phases

i) melting curve : shared between liquid and solid phase of water

ii) vapour curve : shared between liquid and gas phase

iii) sublimation curve: shared between solid and gas phase of water

c) area : these are the portions of a phase diagram which represent single phase of water : solid, liquid or gas

Thus answer is :

Curves are used to indicate that the solid and liquid states of water can exist in equilibrium

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.

the answer is option a.