For statements I and II, state for each if they are true or false. I) Transition metal compounds are often white. II) Transition metals frequently possess completely filled d subshells. If both are true, state if II is a correct explanation for I.
In this question, we are being asked about transition metals. Elements in the periodic table that correspond to the d subshells filling are called d-block elements. The first row of the d-block elements is shown in the diagram colored in pink. However, not all d-block elements count as transition metals. The definition of a transition metal is an element which forms one or more stable ions which have incompletely filled d subshells.
On the basis of this definition, we can exclude scandium and zinc from the transition metals. Although scandium and zinc are d block elements, scandium forms a stable three plus ion which has the electronic configuration identical to argon. Scandium three plus has no d electrons, so does not meet our definition for a transition metal. Zinc forms a stable zinc two plus ion. In the configuration for the zinc two plus ion, zinc has a full d subshell here, so again does not meet the definition for a transition metal either. Notice also how the 4s electrons are lost before the 3d electrons, when these d block elements form ions. So based on this definition, statement II is clearly false.
Compounds containing transition metals with partly filled d orbitals have the ability to absorb certain wavelengths of visible light. The energy is absorbed by electrons being promoted from one energy level to another within the d orbitals themselves. White light is a continuous part of the electromagnetic spectrum containing a range of colors. A solution which appears blue is in fact absorbing the red part of the visible spectrum. If we were to look at a solution of copper sulfate solution, which appears blue, we are seeing the complimentary color of the pulse of the visible spectrum that is being absorbed. That is the red part of the visible spectrum in this case.
In fact, transition metals frequently display a range of colors in their compounds. For example, copper two plus compounds are blue. Iron three plus compounds are frequently orange or brown. Nickel two plus compounds are frequently green. And cobalt two plus compounds are frequently pink. Due to the wide range of oxidation states displayed by transition metals in their compounds, many other colors are possible.
In complete contrast, nearly all compounds of group one and group two metals are white or colorless. Interestingly, compounds containing zinc two plus ions and scandium three plus ions, which are considered d-block elements however they are not transition metals, are also white or colorless. So transition metal compounds are rarely white and frequently display a range of different colors in their compounds. Statement I is therefore false. Since both statements are false, neither is a correct explanation for the other.