Which of the following concept was proposed in Dalton’s atomic theory?

According to  Dalton's theory, all atoms of a specific element are identical in mass, size, and other properties.

Therefore the concept of atomic mass was proposed by Dalton's atomic theory.

The postulates of Dalton's atomic theory are

• All matter is made up of tiny, indivisible particles called atoms.
• All atoms of a specific element are identical in mass, size, and other properties. However, atoms of different elements exhibit different properties and vary in mass and size.
• Atoms can neither be created nor destroyed. Furthermore, atoms cannot be divided into smaller particles.
• Atoms of different elements can combine with each other in fixed whole-number ratios in order to form compounds.
• Atoms can be rearranged, combined, or separated in chemical reactions.