The correct order of seaports from south to north is:
- Singapore (ii) – located at the southernmost of the options.
- Hong Kong (iv) – located slightly to the north of Singapore.
- Shanghai (i) – located further north, in China.
- Yokohama (iii) – located at the northernmost, in Japan.
Hence, the correct sequence is (ii), (iv), (i), and (iii), which corresponds to option (B).