Question
What valencies will be shown by the elements A, B, C, D and E having atomic numbers 2, 4, 8, 10, and 13 respectively.
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| Element | A | B | C | D | E | F |
| Atomic number | 1 | 3 | 8 | 18 | 20 | 1 |
| Mass number | 2 | 7 | 16 | 40 | 40 | 4 |