Define the following terms:
$1.$ Collision
$2.$ Frequency of collision

(N/A) $1.$ Collision: $A$ collision is defined as the interaction between two or more reactant molecules that results in a chemical reaction,provided the molecules possess sufficient kinetic energy (activation energy) and the correct orientation.
$2.$ Frequency of collision: The collision frequency $(Z)$ is defined as the total number of collisions occurring per unit volume per unit time in a chemical reaction mixture.