Q.Comment on the reactions of dihydrogen with

Dihydrogen can act as an oxidising agent (accepting electrons, H → H⁻) or as a reducing agent (losing electrons, H → H⁺), depending on the electronegativity of the partner element.

1. With chlorine — Cl is more electronegative than H, so H2 is oxidised (loses electron density) while Cl2 is reduced. This is a simple radical addition/combination reaction, often initiated by light or heat:

   $H_2(g) + Cl_2(g) \rightarrow 2HCl(g)$

   Here hydrogen goes from the 0 oxidation state to +1 in HCl.
2. With sodium — Na is less electronegative (more electropositive) than H, so here dihydrogen behaves as an oxidising agent: it accepts an electron from Na and is reduced to the hydride ion H⁻, while Na is oxidised to Na⁺. The product is the ionic (saline) hydride sodium hydride:

   $H_2(g) + 2Na(s) \xrightarrow{\Delta} 2NaH(s)$

   Hydrogen goes from 0 to −1 oxidation state. …

Identify which element is more electronegative than hydrogen to decide whether H2 is oxidised or reduced in each reaction, then balance …

• Assuming dihydrogen is always a reducing agent — with reactive metals (Na, Ca) it is actually reduced (oxidising role). …