The problem of position of isotopes in the periodic table was
avoided by arranging elements is ascending order of __________.

Explanation

To solve the question regarding the arrangement of elements in the periodic table and the problem of isotopes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Isotopes**:
- Isotopes are atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons, resulting in different atomic masses.

2. **Periodic Table Arrangement**:
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