# The Solid State

Question 25

## What type of substances would make better permanent magnets, ferromagnetic or ferrimagnetic, justify your answer.

Solution
Ferromagnetic substances would make better permanent magnets.In solid state, the metal ions of ferromagnetic substances are grouped together into small regions called domains. Thus, each domain acts as a tiny magnet. In an unmagnetised piece of a ferromagnetic substance the domains are randomly oriented and their magnetic moments get cancelled. When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field  and a strong magnetic effect is produced. This ordering of domains persist even when the magnetic field is removed and the ferromagnetic substance becomes a permanent magnet.
Question 26

## how many  the number of tetrahedral and octahedral voids are present in a cubic close packed structure of A spheres?

Solution
In ccp structure of a sphere there is 2A tetrahedral voids and A octahedral voids.
Question 27

## What would be the number of tetrahedral and octahedral voids,In a face centred cubic unit cell (i.e., ccp structure) 4 atoms/ions are present?

Solution
there is 8 tetrahedral voids and 4 octhahedral  voids in a face centred cubic unit cell.
Question 28

Solution
Frenkel defect.