How many electrons does a single hydrogen gain or lose in the following reaction? H 2 + O 2 → H 2 O

A. Gain 2

B. Lose 1

C. Gain 1

D. No change

option B. Lose 1.

Explanation:

To determine the number of electrons that a single hydrogen gains or loses you need to realize that the chemical reaction is an oxidation-reduction (redox) reaction and state the changes in the oxidation states.

The substance that gains electrons is being reduced, reducing its oxidation number, and the substance that lose electrons is being oxidized, increasing its oxidation state.

1) State the oxidation state of hydrogen atoms in the rectant side:

H₂: the oxidation state of any element in its atomic or molecular form is zero. That is indicated as a superscript to the right of the chemical symbol: H₂⁰

2) State the oxidation state of the hydrogen atoms in the product side:

H₂O: the rule says that the oxidation state of oxygen, when combined with other elements, except in the case of peroxides, is - 2.

Hence, in order to the molecule H₂O be neutral, the total charge contributed by the two atoms of hydrogen must be + 2: + 2 - 2 = 0.

Since there are two hydrogen atoms, each contributes + 2 / 2 = + 1 charge.

3) Conclusion:

Every atom of hydrogen changes from a 0 oxidation number to a + 1 oxidation number, which, in turn, means that every hydrogen atom loses one electron.

Thus, the answer is, the option B. Lose 1.