What is the second most abundant element in earths crust? a. magma b. oxygen c. silicon d. carbon

Which process does not require the presence of a physical substance in order to transfer heat? air in the atmosphere is heated by the ground. this warm air then rises, and cooler air falls. this is an example of what type of process? how is conduction different from radiation?

Which compound contain an iron with a 3+ charge

The excretory system, need answers for all: )