The electromagnetic spectrum is divided into different regions based on frequency ranges. Let's match the entries:
- X-rays (A) have frequencies in the range of \( 1 \times 10^{16} \, \text{Hz} \) to \( 3 \times 10^{21} \, \text{Hz} \), matching with List II entry I.
- Microwaves (B) have frequencies in the range of \( 1 \times 10^{9} \, \text{Hz} \) to \( 3 \times 10^{11} \, \text{Hz} \), matching with List II entry II.
- Radiowaves (C) have frequencies in the range of \( 5 \times 10^{5} \, \text{Hz} \) to \( 5 \times 10^{9} \, \text{Hz} \), matching with List II entry IV.
- Gamma rays (D) have frequencies in the range of \( 1 \times 10^{18} \, \text{Hz} \) to \( 5 \times 10^{22} \, \text{Hz} \), matching with List II entry III.
Thus, the correct answer is:
\[
\text{A-I, B-II, C-IV, D-III}
\]