Question

Which of the following is a point imperfection                 

         1. Vacancy

         2. Interstitial

         3. Frenkel imperfection

         4. Schottky imperfection

         (a) 1 and 2 only              (b) 2 and 3 only

         (c) 2, 3 and 4 only          (d) 1, 2, 3 and 4