Threshold frequency = 5.13 x 10^14 Hertz

λ = 5.6 x 10^2 nm = 5.6 x 10^-7 meter

c = 3 x 10^8 m/sec

f = c/λ = 5.36 x 10^14 Hertz this is the frequency of the incoming radiation

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h = 6.63 x 10^(-34) joules sec

hf = 3.56 x 10^-19 joules, this is the energy of the incoming radiation

1 electron volt = 1.602 x 10^-19 joules

Ek = 0.098(1.602 x 10^-19) joules = 1.56 x 10^-20 joules, this is the energy of the emitted electrons

hf = Φ + Ek

Φ = hf - Ek = 3.56 x 10^-19 - 0.156 x 10^-19 joules = 3.4 x 10 ^-19 joules, work function of the metal

Finally the threshold frequency is

f = Φ/h = 3.4 x 10^-19 joules/6.63 x 10^-34 joules sec = 5.13 x 10^14 Hertz

You should care for your metals. Don’t let them be exposed to green radiation.