The number of electrons, protons and neutrons in a species are equal to 18,17 and 20 respectively.  The proper symbol to the species is

Given, Z=17 and A=n+p=20+17=37 ; That represents "Cl"But the no. of electrons = 18(>Z)Hence It is anion and charge = 18-17=1∴The symbol is  Cl - 1737