Which of the following postulate is incorrect regarding Dalton's Atomic Theory?

Options

A. Atoms are indivisible and indestructible
B. All the atoms of an element are not identical to each other. They have different masses and sizes
C. The relative numbers and kind of atoms are always the same in a given compound
D. Chemical reactions only rearrange the way in which atoms are combined , the atoms themselves are not changed

Answer

To determine which postulate of Dalton's Atomic Theory is incorrect, we need to review the key postulates of the theory:

1. **All matter is composed of extremely small particles called atoms.**
2. **All atoms of a given element are identical in mass and properties.**
3. **Atoms cannot be subdivided, created, or destroyed in chemical reactions.**
4. **Atoms of different elements can combine in simple whole-number ratios to form chemical compounds.**
5. **In chemical reactions, atoms are combined, separated, or rearranged.**

Now, let's analyze the statements one by one to identify the incorrect postulate:

### Step 1: Analyze the Postulates
- **Postulate 1**: This is correct. Matter is indeed composed of atoms.
- **Postulate 2**: This is the postulate that is often considered incorrect. While atoms of a given element may have the same number of protons, they can differ in mass (isotopes). Therefore, not all atoms of an element are identical.
- **Postulate 3**: This is correct. Atoms are not created or destroyed in chemical reactions; they are merely rearranged.
- **Postulate 4**: This is correct. Atoms of different elements can combine in simple ratios to form compounds.
- **Postulate 5**: This is correct. Chemical reactions involve the rearrangement of atoms.

### Conclusion
The incorrect postulate regarding Dalton's Atomic Theory is the second one: "All atoms of a given element are identical in mass and properties."