Her behavior has been reinforced (i.e. strengthened). Reinforcement can be external or internal and can be positive or negative. If a child wants approval from parents or peers, this approval is an external reinforcement, but feeling happy about being approved of is an internal reinforcement.
It remained to define the unit of amount of substance by fixing the corresponding mass of carbon 12; by international agreement, this mass has been fixed at 0.012 kg, and the unit of the quantity amount of substance was given the name mole (symbol mol).
Chemists often use a unit called the mole to measure quantities. A mole is defined as 6.022 x 10 to the 23rd atoms or molecules of a substance. When the substance is dissolved, the concentration or number of moles of substance per liter of solvent is called the molarity.