Which of the following proves that law of definite proportions is not universally true?

Options

A. The discovery of multiple compounds formed between the same two elements
B. The discovery of non-stoichiometric compounds
C. The discovery of networked solids
D. The discovery of salt-like carbides

Answer

To determine which option proves that the Law of Definite Proportions is not universally true, we first need to understand what the Law of Definite Proportions states.

### Step-by-Step Solution:

1. **Understanding the Law of Definite Proportions**:
- The Law of Definite Proportions, also known as the Law of Constant Composition, states that in a given chemical compound, the elements are always present in a fixed ratio by mass, regardless of the source or method of preparation.

2. **Identifying Limitations of the Law**:
- The law has certain limitations where it does not hold true:
- **Isotopes**: When different isotopes of an element are involved, the mass ratios can vary.
- **Different Compounds**: When elements combine in the same ratio but form different compounds, the law does not apply.
- **Non-stoichiometric Compounds**: These compounds have variable compositions, meaning the ratio of elements can fluctuate within a certain range.

3. **Analyzing the Options**:
- We need to evaluate the provided options to see which one indicates a situation where the Law of Definite Proportions does not hold true.
- **Option 1**: Discovery of multiple compounds formed between the same two elements. This does not prove the law is not universally true; it simply shows that compounds can vary.
- **Option 2**: Discovery of non-stoichiometric compounds. This is a valid limitation of the law, as these compounds do not have a fixed composition.
- **Option 3**: Discovery of network solids. This does not directly relate to the law's validity.
- **Option 4**: Discovery of salt-like carbides. This also does not prove the law is not universally true.

4. **Conclusion**:
- The correct answer is **Option 2: The discovery of non-stoichiometric compounds**. This option directly demonstrates a scenario where the Law of Definite Proportions is not universally applicable.