The work function of the metal is obtained as 5.1 eV
The cutoff frequency is the frequency below which photo electric effect can not occur as electrons are not removed from the metal surface.
Now;
fo = 1.22 x 10^15 Hz
Wo = hfo
Wo = 6.6 * 10^-34 * 1.22 x 10^15
Wo = 8.1 * 10^-19 J
If 1 eV = 1.60 x 10-19 J
x eV = 8.1 * 10^-19 J
x = 8.1 * 10^-19/ 1.60 x 10-19
x = 5.1 eV
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