Correct Answer - C
The complete electronic configuration of Cs is `1s^(2)2s^(2)2p^(6)3d^(6)3d^(10) 4s^(2)4p^(6)4d^(10)5s^(2)5p^(6)6s^(1)` and with noble gas coore is `[Xe] 6s^(1)`.
The general electronic configuration of alkali metals is `["noble gas"] ns^(1)`. Because of similar valence shell electronic configuration, alkali metals possess similar chemical properties and exhibit regular gradation on moving down the group.
