51.

The radius of Na⁺ is 95 pm and that of Cl^- ion is 181 pm. Hence, the coordination number of Na⁺ will be

• 4

• 6

• 8

• unpredictable

The wavelengths of electron waves in two orbits is 3: 5. The ratio of kinetic energy of electrons will be

• 25: 9

• 5: 3

• 9: 25

• 3: 5

Electrons with a kinetic energy of 6.023 x 10⁴ J/mol are evolved from the surface of a metal, when it is exposed to radiation of wavelength of 600 nm. The minimum amount of energy required to remove an electron from the metal atom is

• 2.3125 x 10^-19 J

• 3 x 10^-19 J

• 6.02 x 10^-19 J

• 6.62 x 10^-19 J

A nuclear reaction of ${}_{92}{}^{235}\mathrm{U}$ with a neutron produces ${}_{36}{}^{90}\mathrm{Kr}$ and two neutrons. Other element produced in this reaction is

• ${}_{52}{}^{137}\mathrm{Te}$

• ${}_{55}{}^{144}\mathrm{Cs}$

• ${}_{56}{}^{137}\mathrm{Ba}$

• ${}_{56}{}^{144}\mathrm{Ba}$

On an X-ray diffraction photograph the intensity of the spots depends on:

• neutron density of the atoms/ions

• electron density of the atoms/ions

• proton density of the atoms/ions

• photon density of the atoms/ions

The energy of hydrogen atom in its ground state is -13.6 eV. The energy of the level corresponding to the quantum number n = 5 is

• -5.4 eV

• -0.54 eV

• -2.72 eV

• -0.85 eV

${}_{90}\mathrm{Th}^{232} \to {}_{82}\mathrm{Pb}^{208}.$ The number of $\mathrm{\alpha }$ and $\mathrm{\beta }$-particles emitted during the above reaction is

• $8\mathrm{\alpha } \mathrm{and} 4\mathrm{\beta }$

• $8\mathrm{\alpha } \mathrm{and} 16\mathrm{\beta }$

• $4\mathrm{\alpha } \mathrm{and} 2\mathrm{\beta }$

• $6\mathrm{\alpha } \mathrm{and} 4\mathrm{\beta }$

A near UV photon of 300 nm is absorbed by a gas and then re-emitted as two photons. One photon is red with wavelength 760 nm. Hence, wavelength of the second photon is

• 1060 nm

• 496 nm

• 300 nm

• 215 nm

What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition, n = 4 to n = 2 of He⁺ spectrum?

• n = 4 to n = 2

• n = 3 to n = 2

• n = 2 to n = 1

• n = 4 to n = 3

What is the degenercy of the level of H-atom that has energy $\left(-\frac{{\mathrm{R}}_{\mathrm{H}}}{9}\right)$ ?

• 16

• 9

• 4

• 1