How many variables should be manipulated in a correctly performed scientific experiment?
a) one
b) three
c) two
d) zero

The correct option is A) one

Explanation:

Through scientific experiments, we can test the effect of a certain variable. In a scientific experiment, a dependent variable can be described as the variable which is changed by the scientists so that its effect can be studied on the dependent variable. It is ideal if only one variable is changed at a time. If more than one variable is changed, then it will be difficult to understand which variable brought about the change which is being seen or depicted. Hence, only one variable should be changed while performing a scientific experiment.

answer; both surfaces of the membrane are nonpermeable