Atoms of chemical elements having same atomic mass but a different atomic number are called Isobars. The sum of the number of protons and neutrons together form the atomic mass. Therefore, we can also say the number of nucleons present in the nucleus is equal to the atomic mass of an atom. It will have the same number of nucleons. The number of protons and neutrons alone will vary but the number of nucleons or the sum of protons and neutrons in isobars will always be same. Isobars always have different atomic structure because of the difference in atomic numbers. The number of neutrons makes up the difference in the number of nucleons. Therefore, they are always different chemical elements having same atomic masses. Thus, isobar has different chemical properties. For example : Iron and nickel have atomic number 26 and 28 respectively. However, the mass number is 58. Argon and calcium with atomic number 18 and 20, respectively. However, they have the same atomic mass 40.
Answer : When we increase the temperature of the solid, we are giving energy to it. That energy is utilized in increasing the kinetic energy of the particles and as a result, the speed of the particles is increased and they vibrate more freely. Once the particles overcome the force of attraction between them they start moving more freely.