The correct option is D Adultery
The word for the phrase 'Practice of a married person having an extra marital relationship' is 'Adultery', Option D. Option A 'Polygamy' is. the practice of having more than one wife or husband at the same time. Option B 'Puberty' means time when one reaches sexual maturity. Option C 'Lechery' is lustfulness. Thus, the options A, B and C are incorrect and the correct option is Option D, Adultery.