Killing germs could be placed in a number of sub-branches of science. But the two major banches would be Biology and Chemistry as non-biological chemical agents such as isopropanol or chlorine and other antiseptics/disinfectants are used to break down the biological organisms of microscopic bacteria.
The phenomenon of buoyancy would be classified under the category of hydraulics.
Batteries come under Chemistry, which is a subset of Physics.
It falls under physics along with gravity.
The motion of a basketball falls under the heading of kinematics.
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The study of rocks belongs under the geology branch of science.
gas
This is not a branch of agriculture but a branch of medial science.
Geography
Rheumatology.
Earth science
It falls under Marine Science since ichthyology is the study of fish.
physical and biological
Organic chemistry
The study of insects.
There is no particular branch which deals with extinction, but it would fall under zoology,
Veterinary medicine is its own branch of science, but it comes under both the medical sciences and zoology, a division of biology.