$a, b, c, d$ are electromagnetic radiations. Frequencies of $a, b$ are $3 \times 10^{15} \mathrm{~Hz}, 2 \times 10^{14} \mathrm{~Hz}$, respectively, whereas wavelength of $c, d$ are $400 \mathrm{~nm}, 750 \mathrm{~nm}$, respectively. The increasing order of their energies is

The number of electrons with magnetic quantum number, $m_l=0$ in the elements with atomic numbers $Z=24$ and $Z=29$ are respectively.

Which of the following represents the wavelength of spectral line of Balmer series of $\mathrm{He}^{+}$ion?

$(R=$ Rydberg constant, $n>2)$

The work functions (in eV ) of $\mathrm{Mg}, \mathrm{Cu}, \mathrm{Ag}, \mathrm{Na}$ respectively are $3.7,4.8,4.3,2.3$. From how many metals, the electrons will be ejected if their surfaces are irradiated with an electromagnetic radiation of wavelength 300 nm ?

$\left(h=6.6 \times 10^{-34} \mathrm{Js}, 1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J}\right)$