Which one of the following statements is correct?

Hydrogen exhibits multiple oxidation states depending on its chemical environment. In its elemental form, such as the H2 molecule, the oxidation number of hydrogen is 0. When hydrogen combines with more electronegative non-metals (e.g., in H2O or HCl), it typically assumes an oxidation state of +1. However, when it reacts with less electronegative elements like alkali or alkaline earth metals to form metal hydrides (e.g., NaH or CaH2), it acts as a hydride ion (H-) with an oxidation state of -1 [2]. This variability is due to hydrogen's unique position and electronegativity, allowing it to either lose, gain, or share electrons to fill its 1s shell. Consequently, statements claiming its oxidation number is 'always' a single value are incorrect, making the fourth option the only accurate description.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > What you have learnt > p. 56