[taroicecream]

i've been stumped on this question, so i was hoping i could receive some guidance?

which of the following does not react with 1M NaOH?
MnO(OH)2
Cr(OH)3
MnO2
Al(OH)3
Cr(OH)2

i'm not completely sure how to approach this
for example i know that Al(OH)3 can act as an acid and make [Al(OH)4]-
but i'm not sure how you can tell