Option-wise explanation

1. Cadmium
   Some plants (for example Thlaspi/Noccaea caerulescens) are classic hyperaccumulators of cadmium and zinc, but Chinese brake fern is not primarily used for Cd hyperaccumulation.

2. Arsenic – correct
   Chinese brake fern (Pteris vittata) was the first plant identified as a natural arsenic hyperaccumulator. It can store very high concentrations of arsenic in its fronds (over 1–2% of dry weight) and is widely used for phytoremediation of As‑contaminated soils and waters.

3. Lead
   Some species in other families (e.g., certain Brassica or Helianthus spp.) show lead accumulation, but Pteris vittata is known specifically for arsenic, not Pb.

4. Chromium
   There are plants explored for chromium uptake or stabilization, yet the signature trait of Chinese brake fern is arsenic, not chromium, hyperaccumulation.

Therefore, Chinese brake fern (Pteris vittata) is a hyperaccumulator of arsenic (option 2).