The correct option is C K + hv
Maximum kinetic energy of photo electrons K=Ei−ϕ
where ϕ is the work function of aluminum.
Case 1 :
Incident energy of photon Ei=hv
∴ K=hv−ϕ
We get ϕ=hv−K
Case 2 :
Frequency of the incident photon is doubled, so energy of incident photon also gets doubled.
Thus incident energy of photon Ei=2hv
∴ K′=2hv−ϕ
⟹ K′=2hv−(hv−K)=K+hv