The main reserves of phosphorus in the biosphere is in the

hydrosphere
troposphere
lithosphere
atmosphere

The correct answer is C. lithosphere.

The lithosphere is the solid, outermost shell of a planet or natural satellite. It is composed of the crust and the uppermost mantle. The lithosphere is relatively cool and rigid, and it forms the plates that make up the Earth’s crust.

The lithosphere is the main reservoir of phosphorus in the biosphere. Phosphorus is a vital element for life, and it is found in all living things. Phosphorus is used in the formation of bones and teeth, and it is also involved in energy production and cell signaling.

The lithosphere contains phosphorus in the form of phosphate rocks. Phosphate rocks are formed when the remains of marine organisms are buried and subjected to heat and pressure. Phosphate rocks are mined and used to produce fertilizer.

The other options are incorrect. The hydrosphere is the water on Earth’s surface. The troposphere is the lowest layer of Earth’s atmosphere. The atmosphere is the layer of gases that surrounds Earth.