Which of the following could Werner’s theory not explain?

The correct answer is Option (4) → All of the above

Werner’s theory described the primary and secondary valences of a metal ion and the formulas of complexes, but it did not explain why the bonds form as they do. Each option is one of the questions it left open:

• The colour of complexes — not explained. Colour comes from the absorption of visible light, so it is one of the optical properties of coordination compounds.

• The directional properties of the bonds — not explained. Why the bonds point in fixed directions was left open.

• The magnetic properties — not explained. The characteristic magnetic properties were also left open.

Since Werner’s theory could explain none of the three, the answer is all of the above.

NCERT (2026-27 edition):
5.5 Bonding in Coordination Compounds – “Werner was the first to describe the bonding features in coordination compounds. But his theory could not answer basic questions like:
(i) Why only certain elements possess the remarkable property of forming coordination compounds?
(ii) Why the bonds in coordination compounds have directional properties?
(iii) Why coordination compounds have characteristic magnetic and optical properties?”