WordNet sense 1 (having only a limited ability to react chemically; chemically inactive):

inert, neutral

WordNet sense 2 (not reacting chemically):

unreactive

WordNet sense 3 (characterized by a lack of partiality):

unbiased, unbiassed

WordNet sense 4 (showing lack of favoritism):

impartial

WordNet sense 5 (being neither good nor bad):

so-so

WordNet sense 6 (marked by a lack of interest):

apathetic

WordNet sense 7 ((often followed by `to') lacking importance; not mattering one way or the other):

immaterial

WordNet sense 8 ((usually followed by `to') unwilling or refusing to pay heed):

deaf

WordNet sense 9 (marked by or paying little heed or attention):

heedless, unheeding

WordNet sense 10 (lacking in interest or care or feeling):

unconcerned