Wave picture of radiation state that incident energy is uniformly distributed among all the electrons continuously. Let us first calculate the total number of recipient electrons in 5 layers of sodium.
Consider each sodium atom has one electron free as conduction electron.
Effective atomic area = 10–20m2
Number of conduction electrons in 5 layers
n =

5×area‌of‌each‌layer

effective‌area‌of‌each‌atom

or n =

5×2×10−4

10−20

= 1017
Incident power = incident intensity × area = 10–5×2×10–4 = 2 × 10–9 W
As incident energy is equally distributed among all conduction electrons.
Energy to each conduction electron per second =

2×10−9

1017

= 2 × 10−26 W
Time required for emission by each electron
t =

total‌work‌function‌energy

energy‌received‌per‌second

t =

2eV

2×10−26W

=

2×1.6×10−19

2×10−26

= 1.6 × 107 s = 0.5 year
where experimental observation shows that emission of photoelectrons is instantaneous ≈ 10–9 sec
Thus, wave picture fails to explain photoelectric effect.