In general a scientist who studies chemicals is known as a Chemist although they many be called more accurately by one of any number of more precise titles.
A scientist who studies water (H2O) would be a hydrologist or a water chemist.
A scientist who studies crystals is known as a Crystallographer.
Chemist or Physicist
A scientist who studies matter is called a physicist. Physicists explore the properties and behavior of matter and energy through research and experimentation.
Reactants.
A scientist who studies animals is called a zoologist.
oceanographer
a chemist
The name of a scientist that studies sports is called a sports scientist.
An arachnologist
A virologist is a scientist who studies viruses.
A scientist who studies radioactivity is called a nuclear physicist or a radiologist.
A scientist who studies animal life is a zoologist. There is no particular name for a scientist that specialises in platypuses.
The name for this type of scientist is a teuthologist
This answer is a entomologistA scientist who only studies fish is called an ichthyologist.
Astronomer
environmentalist