Question

which condition is necessary for water droplets to condense and form clouds? dry air ice crystals in air tiny particles in air rising temperatures

Explanation:

When water vapor in the air cools, it needs tiny particles (called condensation nuclei) to condense onto. Dry air would not support condensation. Ice crystals are more relevant in some cloud - formation processes but not the most fundamental necessary condition here. Rising temperatures would not cause condensation (cooling is needed for condensation).

Answer:

C. tiny particles in air