The aqueous solution of transition metal salt changes colour from pink to blue, when concentrated hydrochloric acid is added to it. The changes in colour is due to:

Options

A. evolution of hydrogen that changes the oxidation state of the metal ion
B. change in the coordination number of the metal ion from 6 to 4 and formation of new species in solution
C. formation of a coordination complex of the metal ion with hydrochloric acid
D. protonation of the metal ion

Answer

B