Question

At what point do the particles of a solid become free from the fixed positions on heating it?
A.Melting point
B.Freezing point
C.Boiling point
D.All of the above.

Answer 1

Different transition temperatures are associated with the different phase changes that take place at that particular temperature. Only the solid state consists of particles being placed in a lattice with fixed positions; particles in the remaining two states are free to move.

Complete answer:
The solid state of matter is the most dense state in which the particles are compactly packed together with minimum intermolecular spaces and strong intermolecular forces of attraction binding them together.
Due to the high forces of attraction and limited thermal energy constituent particles of a solid are trapped in fixed positions and do not show any mobility.
Heating the solid results in an energy transfer from the heat sources to the particles. The particles absorb an excess thermal energy that allows them to move from their fixed positions. The temperature at which this phenomenon occurs is associated with the phase transformation of a solid into a liquid and is known as the melting point.
The freezing point is the same temperature as that of melting point but the phase transformation that occurs at this temperature is the opposite of melting and particles tend to come closer on freezing.
Hence, the correct option is (A) Melting point.

Note:
The boiling point is associated with liquids and not solids, even though the particles at boiling point have enough thermal energy to escape as vapours and get rid of their fixed positions but boiling is a phenomenon that occurs in liquids and not solids.