Classification (resource requirement): Three pairs show a resource required by the second item to function or exist; one pair reverses the direction (source → content). Identify the odd pair.

Introduction / Context:
Many classification questions turn on whether the semantic direction of “requirement” is preserved. Three pairs show a resource needed by an entity; one pair names a source that supplies a resource, flipping the relation.

Given Data / Assumptions:

• Oil is required by a lamp (as fuel) to burn.
• Power is required by a machine to operate.
• Oxygen is required for life processes.
• Water : Tap actually denotes a source → provided substance; a tap dispenses water.

Concept / Approach:
Check whether the first term is a prerequisite to the functioning/existence of the second. If instead the second term is a source that supplies the first, the relation is reversed and becomes the odd one out.

Step-by-Step Solution:

Verification / Alternative check:
Try stating “X is required by Y.” Oil is required by lamp; power by machine; oxygen by life. “Water is required by tap” is false; taps deliver water.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing supply/source relationships with requirement relationships; note the directionality.

Final Answer:
Water : Tap