Answer:
Cs
Step-by-step explanation:
This element is the farthest right, and lowest meaning that its reactivity is very high.
1. valence electrons and electronegativity
2. Both reactivity and electronegativity decrease down a group.
3. Electronegativity decreases down a group and reactivity increases down a group.
4. The number of valence electrons increases from left to right.
5. Cs
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