<h3><u>Answer and explanation;</u></h3>
- <u>Melting point</u> is defined as the temperature at which solid and liquid phases are in equilibrium. It is the temperature at which a solid changes state from solid to liquid at atmospheric pressure.
- <u>Boiling poin</u>t is the temperature at which the vapour pressure of a liquid is equal to the external pressure. It is the temperature at which a substance changes from a liquid into a gas.
- <u>The flash point </u>of a flammable liquid or volatile liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed.
Trees are important because oxygen
Answer: 
Explanation:
The density
of a material is given by:
(1)
Where:
is the mass of the cube
is the volume of the cube
Now, the volume of a cube is equal to the length
of its edge to the power of 3:
(2)
If we know
, the volume of this cube is:
(3)
Substituting (3) in (1):
(4)
This is the density of the cube
B) equal in magnitude but opposite direction