Extension phase of a nuclear family begins with -

phase 1 ; formation - begins with marriege and ends with bih of first child 2; extension - from bih of first child to bih of last child 3 ; complete extension - from bih of last child to 1st child leaves home 4; contraction - from 1st child leaves home to last child leaves home of parents 5; completed contraction - from last child has left home of parents to 1st spouse dies 6; dissolution- from 1st spouse dies to death of survivors ref ;(page no;683)23rd edition of PARK&;s textbook of Preventive and Social medicinel medicine