Salts of which elements are generally coloured:

Options

A. Transition
B. Normal
C. Lanthanides
D. Inner-transition

Explanation

**Step-by-Step Solution:**

1. **Identify the Elements**: The question asks about salts that are generally colored. The elements that typically form colored salts are primarily found in the transition metals, lanthanides, and actinides.

2. **Transition Metals**: Transition metals are located in the d-block of the periodic table. Most of these metals, such as iron (Fe), copper (Cu), cobalt (Co), and manganese (Mn), form colored compounds due to the presence of unpaired d electrons.

3. **Lanthanides and Actinides**: These are the f-block elements. Lanthanides (elements 57-71) and actinides (elements 89-103) also form colored salts because of the f electrons. For instance, compounds of cerium (Ce) and neodymium (Nd) are known to be colored.

4. **Exceptions**: It's important to note that not all d-block elements are colored. For example, zinc (Zn), cadmium (Cd), and mercury (Hg) do not form colored salts as they have a full d subshell and lack unpaired electrons.

5. **Reason for Color**: The color in these salts arises from electronic transitions. When light hits these compounds, electrons can be excited from a lower energy d orbital to a higher energy d orbital. The specific wavelengths of light absorbed during this transition correspond to the colors observed.

6. **Conclusion**: Therefore, the salts of transition metals, lanthanides, and actinides are generally colored, while salts of alkali and alkaline earth metals (like NaCl) are typically colorless.

**Final Answer**: Salts of transition metals, lanthanides, and actinides are generally colored.

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