Q.1. What is the reason of diamagnetism ?

Ans- The presence of paired electrons in the orbitals in the cause of diamagnetism. The pairing of the electrons cancel their magnetic moments and they lose their magnetic behaviour.

Q.2. Why are ionic solids behave as conductor in the molten state and not in the solid state ? Explain.

Ans- In the ionic solids the electrical conductivity is due to the moment of the ions. Since the ionic mobility is negligible in the solid state, these are non-conducting in this state. Upon melting, the ions present acquire some mobility. Therefore, the ionic solids become conductor.

Q.3. What are F-centres in a crystal ?

Ans- A negative ion may be missing its lattice site leaving a hole which is occupied by an electron there by maintain the electrical balance. The sites containing the electrons trapped in the anion vacancies are called F-centres.

Q.4. Why is potassium chloride sometimes violet instead of white ?

Ans- In presence of excess of potassium, Cl ions leave the crystal lattice site of KCl. In doing so, potassium ionises to give k⁺ and e^–.

The anion vacancies are occupied by electrons. These are called F centres and are responsible for violet colour of violet instead of white.

Q.5. A solid is made of two elemets P and Q Atoms of Q are in c.c.p. arrangement while atoms of P occupy all the tetrahedral sites. What is the formula of compound ?

Ans- Let the number of Q atoms in c.c.p. = n

Hence, the number of octahedral voids = number of atoms in ccp .

As the number of tetrahedral sites = 2 * (number of octahedral voids).

Hence, the number of P atom = 2n

Hence the formula of compound is P₂Q.