Anomalous behaviour of oxygen is due to

Explanation

**Step-by-Step Solution:**

1. **Understanding the Group:** Oxygen belongs to Group 16 of the periodic table, which includes sulfur, selenium, tellurium, and polonium. Each of these elements has similar chemical properties, but oxygen exhibits anomalous behavior compared to the others.

2. **Size of Oxygen Atom:** One of the primary reasons for the anomalous behavior of oxygen is its small atomic size. The small size leads to a higher charge density around the nucleus, which affects its bonding and reactivity.

3. **Electron Density:** Due to its small size, oxygen has a high electron density. This means that the electrons are held more tightly to the nucleus compared to larger elements in the same group. This affects its ability to form bonds.

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