The type of variable that can contaminate the results of an experiment and may be an alternative to a causal relationship is known as a(n):

The answer is extraneous variable
an extraneous variable is the type of variables that is impossible to control or properly predicted by the researchers.
For example, in researching life expectancy of a group of animals in a certain region, sudden extreme weather that killed a lot of the animals could be considered as an extraneous variable.