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

Options

A. Atoms are minute, 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 will analyze each of the given postulates one by one.

### Step-by-Step Solution:

1. **Postulate 1: Atoms are minute, indivisible, and indestructible.**
- This postulate states that atoms cannot be divided into smaller parts and cannot be destroyed. This is a correct statement according to Dalton's Atomic Theory. Therefore, this postulate is **correct**.

**Hint:** Remember that Dalton believed atoms were the smallest units of matter.

2. **Postulate 2: All the atoms of an element are not identical to each other; they have different masses and sizes.**
- This postulate claims that atoms of the same element can differ in mass and size. However, according to Dalton's Atomic Theory, all atoms of a given element are identical in mass and properties. Therefore, this postulate is **incorrect**.

**Hint:** Dalton's theory emphasizes that atoms of the same element are identical.

3. **Postulate 3: The relative numbers and kinds of atoms are always the same in a given compound.**
- This postulate indicates that in any given compound, the ratio of the atoms is fixed. For example, in water (H₂O), there are always two hydrogen atoms for every one oxygen atom. This statement is **correct** according to Dalton's Atomic Theory.

**Hint:** Think about the fixed ratios in chemical formulas.

4. **Postulate 4: Chemical reactions only rearrange the way in which atoms are combined, and the atoms themselves are not changed.**
- This postulate states that during a chemical reaction, the atoms themselves do not change; they only rearrange. This is also a correct statement according to Dalton's Atomic Theory.

**Hint:** Consider how atoms are conserved in chemical reactions.

### Conclusion:
The incorrect postulate regarding Dalton's Atomic Theory is **Postulate 2**: "All the atoms of an element are not identical to each other; they have different masses and sizes."