Water forms from its elements according to the reaction: 2 h2 + o2 --> 2 h2o. in this reaction, which element is reduced?

Oxygen is reduced while hydrogen is oxidized.

Explanation:

Chemical reaction:

2H₂ + O₂ → 2H₂O

The oxidation state of hydrogen and oxygen in left side is zero while on right side the charge on oxygen is -2 and hydrogen is H₂⁺² . So hydrogen is oxidized and oxygen is reduced.

oxygen is oxidizing agent while hydrogen is reducing agent.

Oxidation:

Oxidation involve the removal of electrons and oxidation state of atom of an element is increased.

Reduction:

Reduction involve the gain of electron and oxidation number is decreased.

Oxidizing agents:

Oxidizing agents oxidize the other elements and itself gets reduced.

Reducing agents:

Reducing agents reduced the other element are it self gets oxidized.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).