Astudent designs an experiment where she will put the same amount of air into three different balloons. one balloon will be submerged in ice water, one
balloon will be carefully heated with a hair dryer, and the last balloon will be left alone. after making the changes, the student then will then measure the diameter of each balloon. the dependent variable is:

a)the temperature of the balloon
b)the diameter of the balloon
c)the amount of air
d)the three balloons

B the diameter of the balloon

the dependant variable is the thing that changes as a result of what has been done to it. in this instance the diameter of the balloon will change once the experiment has been done.

the temperature of the balloon would be the independant variable therefore the answer is not A. (the balloon changes shape as the air expands when heated, or deflates when the temperature decreases)

the amount of air is the control variable as it wouldn't be a fair test if the diameters weren't the same to begin with, so it isnt option B.

i have no clue why option D is there, but it wouldnt make sense that the amount of balloons would change.

therefore the answer is option B

Exothermic,  physical change after it is already baked