(a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts.
(b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.
State Modern periodic law.

Explanation

### Step-by-Step Text Solution:

**(a) Advantages and Limitations of Early Attempts:**

1. **Dobereiner:**
- **Advantage:** Dobereiner arranged elements into groups of three known as triads, where the elements in each triad had similar chemical properties. This was an early attempt to classify elements based on their properties.
- **Limitation:** He was only able to form three triads, which limited the applicability of his classification system to a small number of elements.

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