The wave picture of light has failed to explain which of the following phenomena?

In a photoelectric experiment,a parallel beam of monochromatic light with power of $200 \ W$ is incident on a perfectly absorbing cathode of work function $6.25 \ eV$. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is $100 \%$. $A$ potential difference of $500 \ V$ is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force $F = n \times 10^{-4} \ N$ due to the impact of the electrons. The value of $n$ is. . . . .
Mass of the electron $m_e = 9 \times 10^{-31} \ kg$ and $1.0 \ eV = 1.6 \times 10^{-19} \ J$.

Define threshold frequency and on which factor does threshold frequency depend?

"With increase in frequency of light incident, number of electrons emitted increase" - True or false?

The work functions of Caesium $(Cs)$, Potassium $(K)$, and Sodium $(Na)$ are $2.14 \ eV$, $2.30 \ eV$, and $2.75 \ eV$ respectively. If incident electromagnetic radiation has an incident energy of $2.41 \ eV$, which of these photosensitive surfaces may emit photoelectrons?

Which of the following graphs represents the variation of photoelectric current with the property of light shown on the $x-$axis?