In photoelectric effect, if the energy required to overcome the attractive forces on the electron, (work…
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 $\mathrm{eV}$
$2.52$
$2.20$
$2.35$
$2.01$
Solution
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 $2.20 \mathrm{eV}$.