An electron moving with speed $v$ and a photon moving with speed $c$ have the same de Broglie wavelength. The ratio of the kinetic energy of the electron to that of the photon is -

One day on a spacecraft corresponds to $2$ days on the earth. The speed of the spacecraft relative to the earth is

$A$ photon and an electron have equal energy $E$. The ratio $\lambda_{\text{photon}} / \lambda_{\text{electron}}$ is proportional to:

The correct curve between the stopping potential $(V_s)$ and intensity of incident light $(I)$ is

Some laws/processes are given in Column $I$. Match these with the physical phenomena given in Column $II$.

Column $I$	Column $II$
$(A)$ Transition between two atomic energy levels	$(p)$ Characteristic $X$-rays
$(B)$ Electron emission from a material	$(q)$ Photoelectric effect
$(C)$ Mosley's law	$(r)$ Hydrogen spectrum
$(D)$ Change of photon energy into kinetic energy of electrons	$(s)$ $\beta$-decay

Answer the following questions:
$(a)$ Quarks inside protons and neutrons are thought to carry fractional charges $[(+2/3)e, (-1/3)e]$. Why do they not show up in Millikan's oil-drop experiment?
$(b)$ What is so special about the combination $e/m$? Why do we not simply talk of $e$ and $m$ separately?
$(c)$ Why should gases be insulators at ordinary pressures and start conducting at very low pressures?
$(d)$ Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?
$(e)$ The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations:
$E = h\nu, p = \frac{h}{\lambda}$
But while the value of $\lambda$ is physically significant,the value of $\nu$ (and therefore,the value of the phase speed $\nu\lambda$) has no physical significance. Why?