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