Isomers of a substance must have the same

Options

A. structural of formula
B. physical properties
C. chemical properties
D. molecular formula

Explanation

To answer the question, "Isomers of a substance must have the same...," we need to analyze the concept of isomerism in chemistry. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Isomers**:
- Isomers are compounds that have the same molecular formula but different structural arrangements. This means they contain the same number of atoms of each element but are arranged differently in space.

2. **Molecular Formula**:
- The defining characteristic of isomers is that they share the same molecular formula. For example, both dimethyl ether (CH3OCH3) and ethanol (C2H6O) have the same molecular formula (C2H6O) but differ in structure.

3. **Different Structures**:
- Isomers can have different structural formulas. This means that while they have the same types and numbers of atoms, the way those atoms are connected or arranged differs. For instance, the structural formula of dimethyl ether is CH3OCH3, while that of ethanol is CH3CH2OH.

4. **Physical Properties**:
- Isomers can exhibit different physical properties such as boiling points, melting points, and solubility. For example, ethanol can form hydrogen bonds due to its hydroxyl (OH) group, leading to a higher boiling point compared to dimethyl ether, which cannot form such bonds.

5. **Chemical Properties**:
- The chemical properties of isomers can also differ significantly. Ethanol, having an OH group, can react with sodium to form sodium ethoxide, while dimethyl ether does not have an acidic hydrogen and thus does not react in the same way.

6. **Conclusion**:
- Therefore, the correct answer to the question is that isomers of a substance must have the same **molecular formula** but can have different structures, physical properties, and chemical properties.

### Final Answer:
Isomers of a substance must have the same **molecular formula**.