Question

this substance cannot be separated physically or chemically. atom element solution compound

Explanation:

An atom is the smallest unit of an element that retains the chemical properties of that element and cannot be separated physically or chemically into simpler substances by ordinary chemical means. Elements are composed of atoms. A solution is a homogeneous mixture that can be separated by physical means like evaporation. A compound is composed of two or more elements chemically combined and can be separated chemically.

Answer:

atom