Simplify the following text for a Grade 7 native English-speaking person.
Original: A molecule is achiral ( not chiral ) when an improper rotation , that is a combination of a rotation and a reflection in a plane , perpendicular to the axis of rotation , results in the same molecule - see chirality ( mathematics ) . An equivalent definition is that a chiral molecule lacks a plane of symmetry .
Simplified: A molecule is achiral ( not chiral ) if it has an axis of symmetry .