Which of the following compounds is expected to be coloured?

\(CuF_2\)

The correct answer is option 2. \(CuF_2\).

\(CuF_2\) is a coloured compound because it has one unpaired electron in the d-orbital. When visible light falls on \(CuF_2\), the unpaired electron can be excited to a higher energy d-orbital. This causes the absorption of some of the visible light, and the transmitted light appears to be the complementary color.

The complementary color of blue is yellow, so \(CuF_2\) appears to be yellow. However, the color of \(CuF_2\) can vary depending on the impurities present in the compound. For example, if \(CuF_2\) contains impurities of \(Fe^{2+}\), the color can appear to be green.