Blue colour of blood of molluscs is dur to haemocyanin/phycocyanin.

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks whether the blue color of blood in molluscs is due to hemocyanin or phycocyanin.

2. **Understand Hemocyanin**: Hemocyanin is a protein that functions as an oxygen transporter in the blood of certain invertebrates, including molluscs. It contains copper ions, which are responsible for its blue color when oxygenated.

3. **Understand Phycocyanin**: Phycocyanin is a pigment found in cyanobacteria that contributes to photosynthesis. It also has a blue color but is not involved in the blood of molluscs.

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