Question

What are the variables of Boyle's Law

Answer 1

Boyle's law:
If temperature and the number of gas particles are held constant, pressure and volume are inversely proportional to one another.

PV = constant

It (and Charles' Law) are narrow cases of the ideal gas law:
PV = kNt

Whether P or V are independent or dependent is arbitrary. You could set up an experiment where you steadily vary the volume and measure the pressure. Then you'd say pressure is a function of volume. You could just as easily steadily vary the pressure and measure the volume. Then you'd say volume is a function of pressure. So take your pic. There's no right or wrong answer.