Analogy — Choose the best composition relation: Water : Oxygen

Introduction / Context:
“Water : Oxygen” represents a component-of relation: oxygen is a constituent element of water (H2O). We need an option where the second item is a component element of the first substance.

Given Data / Assumptions:

• Water contains oxygen atoms along with hydrogen.
• We seek a clear composition (whole→part) mapping.

Concept / Approach:
Evaluate whether the second item is a necessary constituent of the first, not merely coexisting or thematically associated.

Step-by-Step Solution:
(a) Helium : Nitrogen → distinct gases, neither composes the other.(b) Salt : Sodium → common salt (sodium chloride) contains sodium; correct component relation.(c) Tree : Plant → class–member inversion (tree is a plant).(d) Food : Hunger → cause–effect relation, not composition.

Verification / Alternative check:
“Water contains oxygen” parallels “salt contains sodium.”

Why Other Options Are Wrong:
(a) Mere co-presence in atmosphere; (c) taxonomy not composition; (d) causality rather than part–whole.

Common Pitfalls:
Confusing class–member or cause–effect with composition.

Final Answer:
Salt : Sodium