The metal that gives hydrogen gas upon treatment with both the acid as well as the base is

Step-by-step solution

(i) M g + H C l → M g C l 2 + H 2 ↑         M g + N a O H → O H 2 + N a (ii) F e + H C l → F e C l 3 + H 2 ↑       F e + 2 O H - → F e O H 2 + 2 N a (iii) Z n is amphoteric in nature, so it reacts with acid as well as base. Z n + H C l → Z nC l 2 + 1 2 H 2 g ↑ Zn + NaOH → ZnO 2 - 2 + H 2 g ↑ (iv) Hg + NaOH → Hg + HgO + H 2 O H g + 2 H C l → H g 2 C l 2 + H 2 ( g )