What is the basic theme of organisation in the periodic table?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Periodic Table**: The periodic table is a systematic arrangement of elements based on their atomic number, electron configuration, and recurring chemical properties.

2. **Classification into Periods and Groups**: The elements are organized into horizontal rows called periods and vertical columns called groups. Each period corresponds to the number of electron shells an atom has, while each group contains elements that exhibit similar chemical properties.

3. **Similar Properties**: The primary theme of the organization is that elements within the same group (column) have similar physical and chemical properties. This similarity arises from their similar valence electron configurations.

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