Consider the spectral line resulting from the transition from n= 2 to n = 1, in atoms and ions given below. The shortest wavelength is produced by

• hydrogen atom

• deuterium atom

• doubly ionized lithium

• doubly ionized helium

The energy of an electron in excited hydrogen atom is −3.4eV. Then according to Bohr's theory, the angular momentum of the electron is

• 2.1 × 10^-34 J-s

• 3 × 10^-34 J-s

• 2 × 10^-34 J-s

• 0.5 × 10^-34 J-s

The solar spectrum during a complete solar eclipse is

• continuous 

• emission line

• dark line

• dark band

A particle of mass M at rest decays into two masses m₁ and m₂ with non zero velocities. The ratio of de-Broglie wavelengths of the particles $\frac{{\mathrm{\lambda }}_1}{{\mathrm{\lambda }}_2}$ is

• $\frac{{\mathrm{m}}_2}{{\mathrm{m}}_1}$

• $\frac{{\mathrm{m}}_1}{{\mathrm{m}}_2}$

• $\frac{\sqrt{{\mathrm{m}}_1}}{\sqrt{{\mathrm{m}}_2}}$

• 1 : 1

For an electron in the second orbit of Bohr's hydrogen atom, the moment of linear momentum is

• $\mathrm{\pi h}$

• $2\mathrm{\pi h}$

• $\frac{\mathrm{h}}{\mathrm{\pi }}$

• $\frac{2\mathrm{h}}{\mathrm{\pi }}$

If elements with principal quantum number n > 4 were not allowed in nature, the number of possible elements would have been

• 32

• 60

• 64

• 4

The spectrum obtained from the chromosphere of the sun at the time of total solar eclipse is

• line emission spectrum

• band emission spectrum

• continuous emission spectrum

• line absorption spectrum

Which state of triply ionised Beryllium (Be⁺⁺⁺) has the same orbital radius as that of the ground state of hydrogen ?

• n = 3

• n = 4

• n = 1

• n = 2

39.

If M is the atomic mass and A is the mass number, packing fraction is given by

• $\frac{\mathrm{M}}{\mathrm{M} - \mathrm{A}}$

• $\frac{\mathrm{M} - \mathrm{A}}{\mathrm{A}}$

• $\frac{\mathrm{A}}{\mathrm{M} - \mathrm{A}}$

• $\frac{\mathrm{A} -\hspace{0.17em}\mathrm{M}}{\mathrm{A}}$

Excitation energy of a hydrogen like ion in its first excitation state is 40.8 eV. Energy needed to remove the electron from the ion in ground state is

• 40.8 eV

• 27.2 eV

• 54.4 eV

• 13.6 eV