In the following question, out of the four alternatives, choose the one which can be substituted for the given definition. The act of killing a whole group of people, especially an entire race.

Introduction / Context:
This vocabulary question tests your knowledge of one word substitutes. You are given a definition: “The act of killing a whole group of people, especially an entire race,” and asked to choose the single word that expresses this idea. Such questions are common in competitive exams because they check both language precision and awareness of important social and historical terms.

Given Data / Assumptions:

• The definition clearly mentions killing.
• It is directed at a whole group of people rather than a single individual.
• The group is especially a whole race or ethnic community.
• The options given are Patricide, Genocide, Parricide and Matricide.
• Each option contains the suffix “cide”, which means killing.

Concept / Approach:
The key to solving one word substitute questions is to break the words into roots and suffixes and recall their specific meanings. The suffix “cide” comes from Latin and means killing. The prefixes “patri”, “matri” and “gen” refer to father, mother and race or kind respectively. By matching the root with the given definition, we can identify the only option that refers to killing a race.

Step-by-Step Solution:
Step 1: Recognise that all options involve killing because of the common “cide” ending. Step 2: Recall that “Patricide” means killing one's father, since “pater” or “patri” relates to father. Step 3: Recall that “Matricide” means killing one's mother, as “mater” or “matri” relates to mother. Step 4: Recall that “Parricide” usually means killing a close relative or parent, often one's father or another near family member. Step 5: “Genocide” combines “geno” (race, people, kind) with “cide” (killing) and therefore means the systematic killing of a large group of people, especially those of a particular nation, race or ethnic group.

Verification / Alternative check:
To verify, compare each option with the definition. Only Genocide refers to killing a whole group or race. Patricide, Matricide and Parricide all refer to killing a particular family member or close relative and not an entire community. The historical use of the word Genocide in describing mass killings in history also matches the description given in the question.

Why Other Options Are Wrong:
Patricide is specific to killing one's father, which does not match the idea of destroying an entire group. Matricide is killing one's mother. Parricide covers the killing of a parent or close relative and is still limited to an individual. None of these options involve a whole race or ethnic group, so they cannot be correct here.

Common Pitfalls:
Students sometimes confuse “Parricide” and “Patricide” because both involve family members, or they may guess based only on sound. Another mistake is to rely purely on vague impressions instead of analysing the roots. Learning the meanings of common roots like “gen”, “bio”, “tele” and “auto” helps you decode many words correctly in exam situations.

Final Answer:
The correct one word substitute is Genocide, so the correct option is Genocide.