Question

Which best defines pressure?
a measure of the number of particles in a unit area
a measure of the force of the collision of particles on a unit area
a measure of the number of particles on the outside of a container
a measure of the force of the collision of particles on the inside of a container

Answer 1

a measure of the force of the collision of particles on a unit area

Reason: pressure is force per unit area (in gases it comes from particles colliding with a surface).