What is the experimental evidence in support of the idea that electronic energies in an atom are quantized?

Explanation

**Step-by-Step Solution:**

1. **Understanding Quantization of Electronic Energies:**
- The concept of quantization in atomic physics means that electrons in an atom can only occupy specific energy levels. They cannot exist in between these levels, which implies that the energies are discrete rather than continuous.

2. **Bright Line Spectrum:**
- One of the primary pieces of experimental evidence for the quantization of electronic energies is the observation of the bright line spectrum (or emission spectrum) of elements. When an atom is excited, its electrons jump to higher energy levels. When these electrons return to their original (lower) energy levels, they emit light at specific wavelengths.

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