why the reactivity of the elements increases down the 1 st group and decreases down in the 17th group?

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Solution

In case of Group- 1
The reactivity of Group- 1 means tendency to lose electron..As we move down the group the electrostatic attraction between the nucleus and outer-electron decreases due to increase in the distance from nucleus of outer electron with increase in size of sub-shell orbital.The element will lose electron more easily. So, finally down the group reactivity increases.

In case of Group- 17

The reactivity of the elements decreases as we move down the group in group 17 in the periodic table. As the reactivity of halogen means its tendency to accept electron because they belong to the class of non-metal. If non-metallic character of elements decreases down the group then tendency to accept the electron decrease and the reactivity decreases. Since with increase in size of the elements down the group the tendency to accept electron decreases thus reactivity decreases for the halogens.

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