Question

If r1 < r2 < r3, and if these resistors are connected in series in a circuit, which one dissipates the most power

Answer 1

All three have the same current, so that is not a factor. Wattage (power) is E*I or i^2 R. The higher the resistance, the more power dissipated. The answer is R3 because it has the highest resistance.
R3 <<<< ===== answer.