I’d say A. They are theoretical in the fact that they have not been observed directly, but have been confirmed to exist through experimentation.
Temperature can change a reaction rate because adding or taking away heat means energy is being added or taken away. When energy is added, the particles speed up, so there is a greater chance of the reactants colliding to form the products, which increases the reaction rate. When energy is taken away, the particles more slower, so they don't collide as easily, which slows down the reaction rate.
Therefore, the answer is D.
Anything with a pH level of 3, 2, or 1.
The electron configuration for cobalt is:
[Ar] 3d7 4s2
