On moving from left to right of the periodic table why does the nucleophicity drcreases and basicity increases....???????????

Nucleophilicity increases down the group.

Reason- size increases down the group and thus the ease to loose electron increases.

Nucleophilicity decreases across a period from left to right.

Reason- as the atomic no. increases effective nuclear charge increases… so nucleas holds the outermost electron tight..not providing it for donation. Just consider halogens they are smallest in size and gain electron rather than loosing it…which decreases their electrophilicity…