What is the ‘philosophical zombies’ argument for property dualism

This is an argument by Chalmers that is used to argue against the physicalist idea of what the mind is. The argument is as follows:

P1. Physicalists argue consciousness is a physical property of the brain. This is because, physicalists argue they have a complete, fundamental truth description of the world, everything can be described necessarily in terms of physical processes.  

P2. Therefore, any identical physical world to this actual world must contain consciousness. This is because if the “complete, fundamental truth description of the world” is necessarily true then it must be true in all possible worlds, including this identical world.

P3. However, I can conceive of a world which is physically identical to this world, but where philosophical zombies exist (beings which are physically identical to humans in every way except they are not capable of having qualia)

P4 If a zombie world is conceivable, then it is metaphysically possible.

P5. Therefore, it is the case that it is metaphysically possible for zombies to exist. This is possible because the properties of consciousness are ontologically distinct from, and cannot be reduced to, physical properties.

C1. Therefore, consciousness is non-physical so physicalism is false. (Chalmers, 2010)