Which of these statements is incorrect regarding the laws of chemical combinations?

Options

A. Combination of elements in ratio by atoms is same as their combination ratio by mass
B. Elements may not combine with each other also. For instance, sodium and potassium don't combine to form compounds.
C. Elements can have multiple valencies
D. Fixed amount of an element should combine with different amounts of another element for law of multiple proportions.

Answer

To determine which statement is incorrect regarding the laws of chemical combinations, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding the Laws of Chemical Combinations**:
- The laws of chemical combinations include the Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions.

2. **Analyzing Each Statement**:
- **Statement 1**: "Combination of elements in ratio by atoms is the same as their combination of ratio by mass."
- **Analysis**: For example, in carbon monoxide (CO), the mass ratio of carbon (C) to oxygen (O) is 12:16, which simplifies to 3:4. The atomic ratio is 1:1. Since the mass ratio (3:4) is not equal to the atomic ratio (1:1), this statement is incorrect.

- **Statement 2**: "Elements may not combine with each other."
- **Analysis**: This is true. For example, sodium (Na) and potassium (K) do not combine to form compounds because they are both alkali metals and do not react with each other.

- **Statement 3**: "Elements can have multiple valencies."
- **Analysis**: This is also true. For instance, oxygen can have multiple valencies (e.g., -2 in water, -1 in peroxides).

- **Statement 4**: "Fixed amount of an element should combine with a different amount of another atom for the law of multiple proportions."
- **Analysis**: This statement is correct. For example, in water (H2O), two hydrogen atoms combine with one oxygen atom, demonstrating the law of multiple proportions.

3. **Conclusion**:
- The only incorrect statement is the first one, which claims that the ratio by atoms is the same as the ratio by mass. Therefore, the answer to the question is that the first statement is incorrect.

### Final Answer:
The incorrect statement regarding the laws of chemical combinations is: "Combination of elements in ratio by atoms is the same as their combination of ratio by mass."