The anode voltage of a photocell is kept fixed. The wavelength λ of the light falling on the cathode is gradually changed. The plate current I of the photocell varies as follows:

Let Current be I and intensity be Iint
Each photon gives rise to one photoelectron. Also, intensity is proportional to incident photons and energy of each photon.
Hence, I ∝ Iint
Iint ∝ E
Energy of a photon, E = hc/λ ⇒ I ∝ 1/λ
Option (c) is the closest approximation of the given equation.