(a) What behavior distinguishes paramagnetic and diamagnetic substances? (b) Why are paramagnetic ions common among transition elements but not main-group elements? (c) Why are colored solutions of metal ions common among transition elements but not main-group elements?

Paramagnetic substances are materials that exhibit a specific type of magnetic behavior because they have unpaired electrons. The presence of these unpaired electrons leads to a net magnetic moment in the material. When a paramagnetic material is placed in a magnetic field, it gets attracted toward the field. This is because the unpaired electrons' magnetic moments align with the external magnetic field, enhancing the material's magnetism.
When the external magnetic field is removed, the alignment of the magnetic moments is lost, and the material no longer acts magnetically. Examples of paramagnetic substances include certain metal ions and some organic molecules with odd numbers of electrons.
In summary, the key points are:

• Presence of unpaired electrons
• Attraction toward an external magnetic field
• Loss of magnetic behavior when the external field is removed

Diamagnetic substances exhibit completely different magnetic behavior compared to paramagnetic substances. These materials have all their electrons paired, meaning there are no unpaired electrons. Because paired electrons have opposite spins, their magnetic moments cancel each other out, resulting in no net magnetic moment.
When a diamagnetic material is placed in an external magnetic field, it is weakly repelled by the field. This repulsion occurs because the induced magnetic moments in the material oppose the external magnetic field. Once the magnetic field is removed, diamagnetic materials return to their non-magnetic state, as there are no permanent magnetic moments.
Key characteristics include:

• All electrons are paired
• Weak repulsion from an external magnetic field
• No net magnetic moment
• Behavior disappears when the external field is removed

Transition elements, often found in the d-block of the periodic table, have unique properties due to their electron configurations. One of the defining characteristics of transition elements is their partially filled d-orbitals, which contribute to several distinctive phenomena.
Firstly, many transition elements exhibit paramagnetic behavior due to the presence of unpaired d-electrons. As a result, these elements and their compounds can be attracted to a magnetic field, unlike main-group elements that usually have paired electrons.
Secondly, transition elements frequently form colored solutions. This coloration arises from the electronic transitions between different d-orbitals. When light strikes these solutions, electrons can absorb energy and move to higher energy levels, causing specific wavelengths of light to be absorbed and others to be reflected or transmitted, producing a visible color.

• Partially filled d-orbitals
• Common paramagnetic behavior due to unpaired electrons
• Colored solutions from electronic transitions

Transition elements thus play a crucial role in many chemical and physical processes, making them essential in various scientific and industrial applications.