Why are K3[Cr(C2O4)3].3H2O, K2[Cu(C2O4)2].2H2O and K3[Fe(C2O4)3].3H2O coloured, whereas K3[Al(C2O4)3.3H2O is colourless?

Explanation:

If a body reflects only a/few color/s of the visible spectrum by absorbing remaining, it appears in that reflected color/s. In case of water, its tri-atomic (2 atoms of hydrogen and one atom of oxygen) structure does not absorb any colors from the visible spectrum of the light. ... Hence water appears colorless while others do absorb

the answer would be a

1. they vary with a higher number because boiling is way hotter than melting