Structure of Atom

Given that
Wave length λ = 300 nm = 300 × 10−9m = 3 × 10−7m
Therefore
E = hv =

hc

λ

=

6.6×10−34×3×108

3×10−7

= 6.6 × 10−19J
E (in eV) =

6.6×10−19

1.6×10−9

= 4.1 eV
For a metal to show photoelectric effect, its work function has to be less than or equal to 4.1 eV. From the given table, the number of metals with work function less than or equal to 4.1 eV are Li, Na, K and Mg. Hence four metals will show photoelectric effect.