AMU Engineering 2019 solved paper Solved Paper

NaCl has octahedral crystal system, therefore co-ordination number of each Na+ and Cl− ion is 6. Co-ordination number of atom is determined that the given atom surrounded by how many numbers of atom. In NaCl, each Na+ ion is surrounded by 6Cl− ions and each Cl− ions is surrounded by six Na+ ions. So, they both show co-ordination number 6.