give reason for the following statement (a)separation of lanthanoid elements difficult ?

Explanation

To explain why the separation of lanthanoid elements is difficult, we can break it down into two main reasons:

### Step-by-Step Solution:

1. **Understanding Lanthanide Contraction**:
- The lanthanide series consists of 15 elements from lanthanum (La) to lutetium (Lu).
- As we move from La to Lu, the atomic number increases, but the increase in atomic radius is not significant. This phenomenon is known as **lanthanide contraction**.
- The contraction occurs because of the poor shielding effect of the f-electrons. As more f-electrons are added, they do not effectively shield the increasing nuclear charge, leading to a smaller size of the ions.
...