Which of the following differentiates photosynthesis from respiration?

The question asks which feature is unique to photosynthesis and not shared with respiration. To answer this, compare the two processes:

Now examine each option:

• "Food is usually broken down" describes respiration, not photosynthesis. It does not differentiate photosynthesis from respiration; it describes respiration itself.
• "Oxygen is usually liberated" is characteristic of photosynthesis only. In photosynthesis, water molecules are split and oxygen is released as a by-product. Respiration does the opposite: it consumes oxygen. This is a clear differentiating feature.
• "It occurs both during the day and night" describes respiration, which is continuous. Photosynthesis requires light and occurs mainly during the day.
• "It occurs in both plants and animals" again describes respiration. Photosynthesis occurs only in organisms with chlorophyll, not in animals.

The liberation of oxygen is the feature that belongs to photosynthesis and sets it apart from respiration.