The correct option is A PH3
When a mixture of calcium carbide and calcium phosphide placed in a container is made to react with water, it produces the gases phosphine and acetylene. This signal produced due to the burning gases is called Holme's signal.
The reactions involved in Holme's signal are:
Ca3P2+6H2O⟶2PH3+3Ca(OH)2
CaC2+2H2O⟶C2H2+Ca(OH)2
Hence, option (b) is correct answer.