Explain the reason behind a colour of some gem stone with the help of example.

Question

$\begin{array}{1 1} \text{(a) The colours are due to the presence of positive metal ions} \\ \text{(b) The colours are due to the presence of representative metal ions} \\ \text{(c) The colours are due to the presence of transition metal ions} \\\text{(d) The colours are due to the presence of inner transition metal ions} \end{array}$