Point defects are present in

Due to vacancy defects,the density of a solid substance .............

Which is the incorrect statement?

Which of the following defects,if present,lowers the density of a crystal?

Which of the following statements are not correct?
$(A)$ Diode is a combination of $n$-type and $p$-type semiconductors.
$(B)$ Silicon or germanium is electron rich impurity.
$(C)$ Phosphorus and arsenic are electron deficient impurities.
$(D)$ Schottky defect decreases the density of the crystal.

Explain metal excess defects.