The element that is a component of the hormone thyroxine is: MCQ with Answer and Explanation

Explanation:
Sunlight is the ultimate source of energy for almost all ecosystems. Photosynthetic autotrophs (plants, algae, cyanobacteria) capture solar energy and convert it into chemical energy, which then flows through the food web. Some deep-sea ecosystems rely on chemosynthesis from hydrothermal vents, but globally, the sun drives the biosphere.

Explanation:
The ozone layer in the stratosphere absorbs most of the Sun's harmful UV radiation. CFCs, not CO₂, cause its depletion. Ozone at ground level is a pollutant. So B is correct.

Explanation:
The sperm cell is the smallest cell in the human body, about 5 µm in length (head). The ovum is the largest (about 100 µm diameter). RBCs are about 7-8 µm, neurons can be up to a meter long. Sperm cells are highly specialized for motility and genetic material delivery.