All of the following are classified as abiotic factors EXCEPT a pH
b. bacteria
b. salinity
d. oxygen concentration.

In the group of terms, the exception to abiotic factors is bacteria (option b).

Explanation:

Abiotic factors correspond to the elements of an ecosystem that are not considered alive, such as soil, wind, temperature, pH, among others.

All living beings in an ecosystem are biotic elements, including microorganisms such as bacteria. The dynamics of living beings influence the ecosystem, just as abiotic factors influence both the biotic elements and the development of the ecosystem.

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex