When NAD+ (nicotinamide adenine dinucleotide) reacts with hydrogen and gains two electrons, it gets reduced to NADH (reduced nicotinamide adenine dinucleotide).

Here's the breakdown:

* NAD+ is the oxidized form of the molecule. It has a positive charge.

* NADH is the reduced form. It has gained two electrons and a proton (H+), resulting in a neutral charge.

The reaction:

NAD+ + 2H+ + 2e- → NADH + H+

This reaction is a crucial part of cellular respiration, where NAD+ acts as an electron carrier. It picks up electrons and hydrogen ions (protons) during the breakdown of glucose, carrying them to the electron transport chain where they are used to generate ATP, the cell's energy currency.