The wavelength of a particular electron transition for $\mathrm{He}^{+}$is 100 nm . The wavelength (in $\AA$ ) of H atom for the same transition is

The energy of second Bohr orbit of hydrogen atom is -3.4 eV . The energy of the fourth Bohr orbit of the $\mathrm{He}^{+}$ ion will be

$a, b, c, d$ 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.