In this one word substitution question from medical vocabulary, choose the single word that best matches the definition a region of injured tissue or skin in which blood capillaries have been ruptured, that is, a bruise.

Introduction / Context:
This vocabulary question asks for a technical or semi technical medical term that corresponds to the everyday word bruise. The phrase in the definition explicitly mentions ruptured blood capillaries under the skin. The candidate must select the word that fits this description accurately, rather than a different type of skin or tissue condition.

Given Data / Assumptions:

• The descriptive phrase is a region of injured tissue or skin in which blood capillaries have been ruptured.
• The parenthetical explanation says a bruise.
• The options include pustule, knurl, contusion, tumour, and scar.
• Only one of these matches the idea of a bruise.

Concept / Approach:
A contusion is a medical term for a bruise. It is caused by a blow or impact that breaks small blood vessels under the skin without breaking the skin surface. Pustule refers to a small blister or pimple with pus. Knurl is a small ridged knob or raised pattern, not a medical injury. Tumour is an abnormal mass of tissue formed by growth of cells. Scar is a mark left on the skin after the healing of a wound. Therefore, only contusion matches the definition given in the question.

Step-by-Step Solution:
Step 1: Focus on key words in the definition: injured tissue, skin, blood capillaries ruptured, bruise. Step 2: Recall that contusion is used in first aid, sports medicine, and medical reports as the technical term for bruise. Step 3: Check pustule and note that it is associated with pus and infection, such as in acne, not with a bruise. Step 4: Check knurl and recognise that it belongs to mechanical or design vocabulary, meaning a small ridged feature on a surface. Step 5: Check tumour and scar, both of which refer to different types of tissue change, either growth or healing marks, rather than a simple bruise.

Verification / Alternative check:
To verify, imagine a medical report after an accident. Doctors may write that the patient has contusions on the arm and leg. In everyday language, we would say the patient has bruises on the arm and leg. This equivalence supports contusion as the correct choice. None of the other words can naturally replace bruise in such a context. For example, saying the patient has pustules from the impact is clearly incorrect.

Why Other Options Are Wrong:
Option a, pustule, is a small inflamed, pus filled lesion on the skin and is typical in infections, not blunt trauma. Option b, knurl, has nothing to do with injuries and is used for textured metal or plastic parts. Option d, tumour, is an abnormal tissue mass, often unrelated to a single impact or ruptured capillaries. Option e, scar, appears after healing and does not describe the fresh injury where blood is pooled under the skin. Therefore only contusion matches the injury described in the question.

Common Pitfalls:
Some students may confuse medical terms because they are not frequently used in everyday speech. Another pitfall is to associate tumour or scar with any visible mark on the body and therefore choose them without reading the detailed definition. To avoid such mistakes, it is important to focus on each keyword in the phrase, particularly capillaries ruptured and bruise, which point strongly to contusion.

Final Answer:
The correct one word substitution for a region of injured tissue or skin in which blood capillaries have been ruptured, a bruise, is contusion, so option c is correct.