Give one word for the sentence :
Mass exterminations of human beings. especially of a particular race or nation

Homicide is the killing of one person by the other and is not mass murder.Therefore, option B is incorrect.Matricide and patricide mean's killing one's mother and father respectively and again is not a method of mass killing.So options C and D are incorrect.Genocide means the deliberate killing of a large group of people, especially those of a particular nation or ethnic group.Thus, option A is correct.