Whichof the statement are ture about the law of chemical combination?

Options

A. Potassium combines with two isotopes of chlorine `.^(35)Cl` and `.^(37)Cl`) to form two samples of `KCl`. Their formation follows the law of definite composition.
B. Different proportion of oxygen in the varius oxidies of sulphur prove the law of multiple proportiens.
C. `H_(2) O` and `H_(2)S` contains `11.11%` hydrogen and `5.88%` hydrogen, respectively, whereas `SO_(2)` contains 50% sulphur. The above data prove the law of reciprocal proportions.
D. In the decomposition of `NH_(3), 2NH_(3) overset(Delta)rarr N_(2) + 3H_(2)`, the ratio of volumes of `NH_(3),N_(2)` and `H_(2)` is `2 : 1 : 3` The above data proves the Gay Lussac law.

Answer

To determine which statements are true about the law of chemical combination, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A**: "Potassium combines with two isotopes of chlorine (35Cl and 37Cl) to form two samples of KCl. Their formation follows the law of definite composition."
- **Analysis**: The law of definite composition states that a chemical compound always contains the same proportion of elements by mass. Since the two isotopes of chlorine have different masses, the mass ratio of potassium to chlorine will differ in the two samples of KCl. Therefore, this statement is **false**.

2. **Statement B**: "Different proportions of oxygen in various oxides of sulfur prove the law of multiple proportions."
- **Analysis**: The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers. For example, in SO2 and SO3, the ratio of the masses of oxygen that combine with a fixed mass of sulfur is 2:3. Therefore, this statement is **true**.

3. **Statement C**: "H2O and H2S contain 11.11% of hydrogen and 5.88% of hydrogen respectively, whereas SO2 contains 50% of sulfur. The above data proves the law of reciprocal proportion."
- **Analysis**: The law of reciprocal proportions states that if two elements combine separately with a fixed weight of a third element, the ratios of the masses in which they do so are either the same or simple multiples of each other. The percentages given can be used to show that the ratios of hydrogen in H2O and H2S can be compared with the sulfur in SO2, thus supporting this law. Therefore, this statement is **true**.

4. **Statement D**: "The decomposition of NH3 (2 NH3 → N2 + 3H2) shows that the ratio of volumes of NH3, N2, and H2 is 2:1:3, which proves Gay-Lussac's law."
- **Analysis**: Gay-Lussac's law states that the volumes of gases involved in a reaction at constant temperature and pressure can be expressed in simple whole number ratios. The ratio of volumes in this reaction (2 volumes of NH3 produce 1 volume of N2 and 3 volumes of H2) is indeed a simple whole number ratio. Therefore, this statement is **true**.

### Conclusion:
- **True Statements**: B, C, and D.
- **False Statement**: A.

### Summary of True Statements:
- Statement B is true.
- Statement C is true.
- Statement D is true.