What determines whether a carbon atom's covalent bonds to other atoms are in a tetrahedral configuration or a planar configuration?

Which is the layer underground where all empty spaces are filled with a combination of air and water ?

The excretory system,need answers for all: )

Inside a flashbulb, oxygen surrounds a thin coil of magnesium. when the flashbulb is set off, a chemical reaction takes place in which magnesium combines with oxygen to form magnesium oxide. which of the chemical equations matches the reaction above? a. mg + o2 mgo2 + energy b. 2mg + o mg2o + energy c. 2mg + o2 2mgo + energy d. mg + o mgo + energy