Question

In the photoelectric effect, if the energy required to overcome the attractive forces on the electron, (work functions) of $Li,Na$ and $Rb$ are 2.41 eV, 2.30 eV and 2.09 eV respectively, the work function of $K$ could approximately be in eV.

• A. 2.52
• B. 2.2
• C. 2.35
• D. 2.01

Answer 1

Answer: (B)

2.2

As the size of the atom (element) increases, the energy required to overcome the attractive force on outermost electron decreases.

$Li,Na,K$ and $Rb$ are the members of the same group and have the following order of size:
$Li<Na<K<Rb$

Thus, the energy in case of $K$ is intermediate of $Rb$ and $Na$, i.e.,

2.30 > $K$ > 2.09 or the energy for $K$ is 2.20 eV.

Hence, option B is correct.