1. Fe2O3, SiO2, Cu2O, CrO3, N2O, CaO

2. Cl(I)

CaCl2 --- Ca(II)

FeCl3 --- Fe(III)

NaCl --- Na(I)

BaCl2 --- Ba(II)

CCl4 --- C(IV)

PCl3 --- P(III)

3.

P2O5 + 3H2O == 2H3PO4

Cr2O3 + 3H2 == 2Cr↓ + 3H2O

2Fe(OH)3 == Fe2O3 + 3H2O

Na2O + H2O == 2NaOH

H2SiO3 == H2O + SiO2