How Redox reaction occurs in `NADH_2 and FADH_2`.

Explanation

`AND^+ + 2e + 2H^+ to NADH + H^+`
`FAD + 2e^- + 2H^+ to FADH_2`.
when `AND^+` (Nicotinamide Adenine Dinucleotide - oxidised form) and FAD (Flavin Adenine Dinucleotide) pick up electrons and one or two hydrogen ions (protons), they get reduced to `NADH + H^+ and FADH_2` respectively. When they drop electrons and hydrogen off they go back to their original form. The reaction in which `NAD^+ and FAD` given (reduction) or lose (oxidation) electrons are called redox reaction (Oxidation reduction reaction). These reactions are important in cellular respiration.