This many #NaCl# units approximately represents #1/3# mole of #NaCl#.
Explanation:
If I have #6.022xx10^23# individual items of stuff (any stuff), I have #1##mol# of stuff by definition. Here, I have #2.1xx10^23# formula units of #NaCl#: i.e.
#(2.1xx10^23" formula units of NaCl")/(6.022xx10^23" formula units of NaCl "mol^-1)##=##??##"moles"#
How many individual #Na^+# and #Cl^-# ions does this represent?