The energy of the incident photon is: \[ E = \frac{1240}{\lambda} = \frac{1240}{550} \approx 2.25 \, \text{eV} \] For the photoelectric effect to occur, the energy of the photon must be greater than the work function of the metal.
For Cs (work function = 1.9 eV):
Since \( 2.25 \, \text{eV} > 1.9 \, \text{eV} \), photoelectric effect is possible for Cs.
For Li (work function = 2.5 eV):
Since \( 2.25 \, \text{eV} <2.5 \, \text{eV} \), photoelectric effect is not possible for Li.
Thus, the answer is \( \boxed{\text{Cs only}} \).
Given below are two statements: one is labelled as Assertion (A) and the other one is labelled as Reason (R).
Assertion (A): Emission of electrons in the photoelectric effect can be suppressed by applying a sufficiently negative electron potential to the photoemissive substance.
Reason (R): A negative electric potential, which stops the emission of electrons from the surface of a photoemissive substance, varies linearly with the frequency of incident radiation.
In light of the above statements, choose the most appropriate answer from the options given below:
The steam volatile compounds among the following are: