51.

A certain metal when irradiated by light (r = 3.2 × 10¹⁶ Hz) emits photoelectrons with twice kinetic energy as did photoelectrons when the same metal is irradiated by light (r = 2.0 × 10¹⁶ Hz). The v₀ of metal is

• 1.2 × 10¹⁴ Hz

• 8 × 10¹⁵ Hz

• 1.2 × 10¹⁶ Hz

• 4 × 10¹² Hz

The radio-isotope used for treatment of thyroid disorders is

• Na-24

• P-32

• Co-60

• I-131

A radioactive element X emits 3$\mathrm{\alpha }$, 1$\mathrm{\beta }$ and 1$\mathrm{\gamma }$-particles and forms ₇₆Y²³⁵. Element X is

• ₈₁X²⁴⁷

• ₈₀X²⁴⁷

• ₈₁X²⁴⁶

• ₈₀X²⁴⁶

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

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

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

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

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