Redox — reduction is gain of electrons / decrease in oxidation number; the hydride ion
“An understanding of the definition of reduction, in terms of gain in electrons or change in oxidation number, was required… that reduction of hydrogen gas produces H⁻ ions and that only sodium hydride contains this anion. The other three… are made when hydrogen… is oxidised.”
Pick a compound. The electronegativity comparison sets whether hydrogen is +1 (oxidised) or −1 (reduced, the hydride ion).
Reduction = gain of electrons = fall in oxidation number. Hydrogen only falls below zero (to −1) when bonded to a metal less electronegative than itself.
Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Chemistry 8873 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.
Made by lookang, using Claude Fable 5. More resources: iwant2study.org