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# The binding energy of electrons in a metal is 250KJ/mol.What is the threshold frequency of metal ?

$\begin{array}{1 1}(a)\;6\times 10^{14}sec^{-1}&(b)\;7\times 10^{14}sec^{-1}\\(c)\;6\times 10^{-10}sec^{-1}&(d)\;4\times 10^{14}sec^{-1}\end{array}$

Binding energy of electron $=250KJ/mol$
Binding energy of one electron =$\large\frac{250\times 10^3}{6.023\times 10^{23}}$J
$\Rightarrow 4.15\times 10^{-19}J$
Binding energy $=hv_0$
$v_0$ is threshold frequency
$4.15\times 10^{-19}=6.625\times 10^{-34}\times v_0$
$v_0=6\times 10^{14}sec^{-1}$
Hence (a) is the correct answer.