In an experiment, the independent variable
attects the dependent variable
should never be changes
changes in response to the dependent veable
is a special type of contro

In an experiment the independent variable is special type of control which is control by the experimenter, and it effect the dependent variable.

Explanation:

In dependent variable:

The dependent variable is the variable which is controlled by the experimenter to check its effect on dependent variable.

Dependent variable:

It is variable which being measured in an experiment and which is directly depend upon independent variable.

The both variables are relate in term of  cause and effect. The independent variable is changed by experimenter and its effect produce in dependent variable is then measure.

For example:

To measure how sleep of student effect the test score. The time for a sleep is given by experimenter it is independent variable which may exceed or decreased. It depend upon experimenter choice but the effect on score is dependent variable which depend upon the time of sleep.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.