Asubstance that speeds up the rate of a chemical reaction is called
a. a catalyst.
b. a lipid.
c. a molecule.
d. an element

in theory, limestone is composed principally of the compound calcium carbonate - caco3, but in reality this compound is deposited in conditions involving a number of other compounds as impurities so it ends up being a mixture of many compounds.

hope this : -)

tony (lordcaos066)

the answer would be b i believe