The limiting line of any spectral series in the hydrogen spectrum is the line when `n_2` in the Rydberg's formula is ………….. .

Explanation

To find the limiting line of any spectral series in the hydrogen spectrum using Rydberg's formula, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Rydberg's Formula**:
The Rydberg formula is given by:
\[
\frac{1}{\lambda} = R \cdot z^2 \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right)
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