The distribution ratio between **3M HCl** and **tri-n-butylphosphate** for **PdCl2** is **2.3** ¹. 

To calculate the percentage of **PdCl2** extracted from a **25.0 mL** of a **7x10^-4 M** solution into **10.0 mL** of **tri-n-butylphosphate**, we can use the following formula:

```
% PdCl2 extracted = (D * V_o / V_a) * 100
```

where `D` is the distribution ratio, `V_o` is the volume of the organic phase, and `V_a` is the volume of the aqueous phase ¹. 

Substituting the given values, we get:

```
% PdCl2 extracted = (2.3 * 10.0 mL / 25.0 mL) * 100 = 9.2%
```

Therefore, approximately **9.2%** of **PdCl2** will be extracted from the given solution into tri-n-butylphosphate ¹.
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