Concept:An element's valency is its combining power, determined by how many electrons it must gain or lose to achieve a stable noble gas configuration.
Explanation:The electronic configuration
2,8,7 shows that the outermost (valence) shell contains
7 electrons.
For stability, an atom usually needs
8 electrons in its outermost shell.
Since it already has
7, it needs to gain just
1 more electron to complete the octet.
Therefore, its combining capacity, or valency, is
1.
This matches option B.
Answer:B.
1