Which formula represents an organic compound? cah2c4h8h2o2p2o5?

Answer is: C₄H₈.

C₄H₈ is hydrocarbon, organic compound consisting only of carbon and hydrogen.

CaH₂ (calcium hydride) is alkaline earth hydride, inorganic compound.

H₂O₂ (hydrogen peroxide) is pale blue, clear, inorganic liquid.

P₂O₅ (phosphorus pentoxide) is white, crystalline solid inorganic compound.