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In photoelectric effect, if the energy required to overcome the attractive forces on the electron, (work functions) of $\mathrm{Li}, \mathrm{Na}$ and $\mathrm{Rb}$ are $2.41 \mathrm{eV}$, $2.30 \mathrm{eV}$ and $2.09 \mathrm{eV}$ respectively, the work function of ' $\mathrm{K}$ ' could approximately be in $\mathrm{eV}$
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The correct answer is:
$2.20$
As the size of atom (element) increases, energy required to overcome the attractive force on outermost electron decreases.
$\mathrm{Li}, \mathrm{Na}, \mathrm{K}$ and $\mathrm{Rb}$ are the members of same group and have the following order of size
$\mathrm{Li} < \mathrm{Na} < \mathrm{K} < \mathrm{Rb}$
Thus, the energy in case of $\mathrm{K}$ is intermediate of $\mathrm{Rb}$ and $\mathrm{Na}$, i.e.,
$2.30 < \mathrm{K}>2.09$
or the energy for $\mathrm{K}$ is $2.20 \mathrm{eV}$.
$\mathrm{Li}, \mathrm{Na}, \mathrm{K}$ and $\mathrm{Rb}$ are the members of same group and have the following order of size
$\mathrm{Li} < \mathrm{Na} < \mathrm{K} < \mathrm{Rb}$
Thus, the energy in case of $\mathrm{K}$ is intermediate of $\mathrm{Rb}$ and $\mathrm{Na}$, i.e.,
$2.30 < \mathrm{K}>2.09$
or the energy for $\mathrm{K}$ is $2.20 \mathrm{eV}$.
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