Modern periodic table is based on the atomic number of the elements. The experiment which proved the significance of the atomic number was

Options

A. Mullikan's oil drop experiment
B. Moseley's work on X-ray spectra
C. Bragg's work on X-ray diffraction
D. Discovery of X-ray by Rontgen

Explanation

To solve the question regarding the experiment that proved the significance of the atomic number in the context of the modern periodic table, we can follow these steps:

### Step 1: Understand the Modern Periodic Table
The modern periodic table is organized based on the atomic number of elements, which is the number of protons in the nucleus of an atom. This organization allows for a systematic arrangement of elements that reflects their chemical properties.

**Hint:** Remember that the atomic number is a fundamental property of an element that determines its position in the periodic table.

### Step 2: Identify Relevant Experiments
We need to evaluate the experiments listed in the question options:
1. **Millikan's Oil Drop Experiment** - This experiment measured the charge of the electron and did not directly relate to atomic numbers.
2. **Mosley's Work on X-ray Spectra** - This work involved the study of X-ray emissions from elements and led to the determination of atomic numbers based on the frequencies of X-rays emitted.
3. **Bragg's Work on X-ray Diffraction** - This experiment focused on the diffraction of X-rays by crystals and is not directly related to atomic numbers.
4. **Discovery of the Atomic Number** - This option is somewhat vague but generally refers to the understanding and identification of atomic numbers.

**Hint:** Focus on the experiment that directly relates to the determination of atomic numbers through empirical data.

### Step 3: Analyze Mosley's Contribution
Henry Moseley conducted experiments that established a clear relationship between the wavelength of X-rays emitted by elements and their atomic numbers. His work showed that the atomic number, rather than atomic mass, should be the basis for the arrangement of elements in the periodic table.

**Hint:** Consider how Moseley's findings changed the understanding of the periodic law and the arrangement of elements.

### Step 4: Conclusion
Based on the analysis, the experiment that proved the significance of the atomic number was Moseley's work on X-ray spectra. This work confirmed that the atomic number is a more fundamental property than atomic mass for the classification of elements.

### Final Answer
The experiment which proved the significance of the atomic number was **Mosley's work on X-ray spectra**.

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