We are quoted a #1*mol*L^-1# concentration, and we are given a volume of #100*mL#...and now in aqueous solution, sodium chloride undergoes the reaction....:
#NaCl(s) rightleftharpoonsNa^(+) + Cl^(-)#
And so #n_"NaCl"="volume"xx"concentration"#
#-=100*cancel(mL)xx10^-3*cancelL*cancel(mL^-1)xx1.0*mol*cancel(L^-1)#
#-=0.10*mol#.
And so in this quantity....there are #0.2*mol# of ions in total...#0.1*mol# with respect to #Na^+# ions, and #0.1*mol# with respect to #Cl^-# ions...
And we multiply this molar quantity by the #"Avocado number"#:
#0.1*molxx6.022xx10^23*mol^-1-=6.022xx10^22# #"sodium ions."#
Happy?
