Q1)What is the coordination no. of each type of ions in a rock-salt type crystal structure? how?

 NaCl has fcc structure. In this structure, each Na⁺ ion is surrounded by 6 Cl^- ions and vice-versa. So the co-ordination number of both Na⁺ ions and Cl^- ions is 6. 

Na⁺ : Cl^- = 6:6  is the cn.   refer  diag. for better understanding