4 NaOH + 3 Ag2IO + 2 CrIII(OH)3 5 H2O + 2 Na2CrVIO4 + 6 Ag0

This is an acid-base reaction (neutralization): NaOH is a base, Cr(OH)3 is an acid.

This is an oxidation-reduction (redox) reaction:

6 AgI + 6 e- 6 Ag0 (reduction)

2 CrIII - 6 e- 2 CrVI (oxidation)

Change the oxidation states