What is a point defect?

Non-stoichiometric cuprous oxide,$Cu_{2}O$ can be prepared in the laboratory. In this oxide,the copper to oxygen ratio is slightly less than $2:1$. Can you account for the fact that this substance is a $p$-type semiconductor?

Assertion : No compound has both Schottky and Frenkel defects.
Reason : Both defects change the density of the solid.

In an ionic crystal,$F$-centers are.....

In spite of long-range order in the arrangement of particles,why are the crystals usually not perfect?

Explain the following term with a suitable example:
$(iv)$ $F$-centres