Increasing order of reactivity among group - 1 elements is `Li < Na < K < Rb < Cs`, whereas among group - 17 elements it is `F > Cl > Br > I`- explain.

Explanation

(a) Increasing order of reactivity among group -1 elements is `Li lt Na lt K lt Rb lt Cs` Explanation:
`rarr` Group -1 elements are Alkali metals.
`rarr` Group -1 elements have the tendency to lose the electrons
`rarr` Group -1 elements forms ionic bonds readily by losing electrons
`rarr` Group-1 elements good reducing agents.
`rarr` Electro positive character increases from top to bottom this is due to increase of size.
(b) Increasing order of reactivity among group -17 elements is `F gt Cl gt Br gt I`
Explanation:
`rarr` These are halogens (Group-17)
`rarr` These have high electronegativity due to small size
`rarr` These have the tendency to gain electrons.
`rarr` In a group from top to bottom electronegativity decrease, due to increase of size.
`rarr` These are oxidising agents and forms ionic bonds by gaining electrons.