Which of the following ideas provided an important step toward a more complete understanding of blackbody radiation?

The theory of blackbody radiation is shown by the equation. E= h×f
Where E = energy of the photon, f is the frequency of photon and h is equal to 6.63 ×10⁻³⁴ J.s in the plank constant. Light exists in form of a bundle of energy which is called photon and its energy is determined by frequency.
Therefore, any emission or absorption of light must involve discrete changes in energy of the system. Light is composed of discrete chunks that must be absorbed as a unit.