What is the key characteristic of an oxidation–reduction reaction?

a. electricity is gained.

b. electricity is lost.

c. electrons are exchanged.

d. electrons are gained.

e. electrons are lost.

The key  characteristic  of oxidation-  reduction   reaction  is electrons   are  exchanged  ( answer  C)

   Explanation

Example  of oxidation - reduction  reaction is

  CH4  +2O2 →   CO2  + 2H2O

  from reaction above C  atom  is oxidized  from  oxidation state -4  to 4.

   On the  other hand O atoms   are reduced  from oxidation state of 0 to  2-.  therefore   there is exchange  of electrons  between  C atoms  and O atoms.

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"the periodic table is arranged in order of atomic number."