Type of sodium? True/false (6)
I believe the answer is:
nature
'type' is the definition.
(thesaurus)
'sodium? truefalse' is the wordplay.
I cannot really see how this works, but
'sodium?' could be 'na' (Na is the chemical symbol for sodium) and 'na' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
(Other definitions for nature that I've seen before include "Motherly" , "All non-artificial phenomena" , "Inborn character; essence" , "Disposition; temper" , "Picturesque countryside" .)