Answer: One formula unit of NaCl consists of one cation, whose chemical symbol is 
 and one anion whose chemical symbol is
 and one anion whose chemical symbol is 

Step-by-step explanation:
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals. 
The cation is formed by the metal sodium which forms 
 and the anion is formed by non metal chlorine which forms
 and the anion is formed by non metal chlorine which forms 
 .
.
For a formula unit of sodium chloride, the charges have to be balanced , thus the valencies of ions are exchanged and the neutral compound result. Thus 
 
 and
 and 
 combine to form neutral
 combine to form neutral 
