Match items in Group $1$ with items in Group $2,$ most suitably.
$$\begin{array}{ll} \textbf{Group 1} & \textbf{Group 2} \\ \text{P LED} & \text{1 Heavy doping} \\ \text{Q Avalanche photodiode} & \text{2 Coherent radiation} \\ \text{R Tunnel diode} & \text{3 Spontaneous emission} \\ \text{S LASER} & \text{Current gain} \end{array}$$
- $\text{P – 1 Q – 2 R – 4 S – 3}$
- $\text{P – 2 Q – 3 R – 1 S – 4}$
- $\text{P – 3 Q – 4 R – 1 S – 2}$
- $\text{P – 2 Q – 1 R – 4 S – 3}$