Which of the following nuclei is most unstable?

• ${}_{20}{}^{40}\mathrm{Ca}$

• ${}_{35}{}^{55}\mathrm{Mn}$

• ${}_{50}{}^{119}\mathrm{Sn}$

• ${}_{13}{}^{30}\mathrm{Al}$

Electron affinity is positive when

• O^- is formed from O

• O^2- is formed from O^-

• O⁺ is formed from O

• electron affinite is always a negative value

A particle 'A' moving with a certain velocity has the de-Broglie wavelength 1 Å. For a particle 'B' with mass 25% of 'A' and velocity 75% of 'A'. The de-Broglie wave length of 'B' will be

• 3 Å

• 5.33 Å

• 6.88 Å

• 0.68 Å

The ratio of de-Broglie wavelengths for electron accelerated through 200 V and 50 V is

• 1:2

• 2:1

• 3:10

• 10:3

The nuclear reaction, ${}_{13}{}^{27}\mathrm{Al} + {}_2{}^4\mathrm{He} \to {}_{14}{}^{30}\mathrm{Si} + {}_1{}^1\mathrm{H}$ is

• nuclear fusion

• nuclear fission

• nuclear transmutation

• artificial radioactivity

n/p ratio during positron decay

• increases

• decreases

• remains constant

• All of these

The element ${}_{90}{}^{232}\mathrm{Th}$ belongs to thorium series. Which of the following will act as the end product of the series?

• ₈₂Pb²⁰⁸

• ₈₂Bi²⁰⁹

• ₈₂Pb²⁰⁶

• ₈₂Pb²⁰⁷

If radius of first Bohr's orbit of hydrogen atom is 'x', then the de-Broglie wavelength of electron in 3rd orbit is nearly

• 2πx

• 6πx

• 9x

• x/3

439.

Which of the following notations shows the product incorrectly?

• ${}_5{}^{10}\mathrm{B} (\mathrm{\alpha }, \mathrm{n}) {}_7{}^{13}\mathrm{N}$

• ${}_{96}{}^{242}\mathrm{Cm} (\mathrm{\alpha }, 2\mathrm{n}) {}_{97}{}^{243}\mathrm{Bk}$

• ${}_7{}^{14}\mathrm{N} (\mathrm{n}, \mathrm{p}) {}_6{}^{14}\mathrm{C}$

• ${}_{14}{}^{28}\mathrm{Si} (\mathrm{d}, \mathrm{y}) {}_{15}{}^{30}\mathrm{P}$

Quantum numbers l = 2 and m= 0 represent the orbital

• d_xy

• d_x²-y²

• d_z²

• d_xz