For three different materials, the variation of the stopping potential `V_0` and the wavelength `lambda` of the incident light is shown by curves a,b and c in fig. which material has maximum work function and which one has least work function ?

Explanation

From the graph, we note that for the given incident light of wavelength `lambda`. The material a has highest stopping potential and material c has lowest stopping potential. As

and stopping potential is the negative potential applied to collector w.r.t emitter to stop the fastest photoelectron to reach the collector. Hence, `V_0` is negative.
Therefore, for the given value of `lambda,V_0propphi_0` (in magnitude). Hence, the work function is maximum for metal a and least for metal c.