C is the answer I’m pretty sure
Answer:
Explanation: A yellow precipitate o lead iodide is formed. see equation of reaction below:
→ 
Th PbI2 is the insoluble yellow precipitate
The answer is A-Gravity. Why? This is because B and C are examples of chemical weathering and not mechanical. Although choice D may seem viable lava intrusion is not a direct cause of mechanical weathering although lava pushing upward may help in aiding mechanical weathering it would not be considered a big enough cause, thus gravity is the correct answer.