171.

Atomic number of an atom is Z and mass number is m, then number of neutrons in its nucleus is

• m − Z

• $\frac{\mathrm{m}}{\mathrm{Z}}$

• m + Z

• m × Z

Nucleus of an atom has

• e and n

• e and p

• p and n

• e, p and n

A nucleus undergoes β-decay. The mass number and  atomic number change as

• mass number and atomic number both increases

• mass number remain same and atomic number increases

• mass number increases and atomic number remain same

• mass number and atomic number both decreases

When a radioactive isotope ${}_{88}\mathrm{Ra}^{228}$ decay in series by the emission of 3$\mathrm{\alpha }$ -particles and a β -particle, the isotope finally formed is

• ${}_{82}\mathrm{X}^{216}$

• ${}_{83}\mathrm{X}^{215}$

• ${}_{88}\mathrm{X}^{216}$

• ${}_{83}\mathrm{X}^{216}$

The activity of a radioactive element decreases to one third of the original activity I₀ , in a period of 9 years. After a further lapse of 9 years, its activity will be

• I₀

• (2/3) I₀

• I₀ / 9

• I₀ / 6

If M_o is the mass of an oxygen isotope ${}_8\mathrm{O}_{17}$, M_p and M_n are the masses of a proton and a neutron, respectively, the nuclear binding energy of the isotope is

• (M_o − 8M_p) c²

• (M_o − 8M_p − 9M_n) c²

• M_oc²

• (M_o − 17M_n) c²

If the bindings energy of the electron in a hydrogen atom is 13.6 eV, the energy required to remove the electron from the first excited state of Li⁺⁺ is

• 30.6 eV

• 13.6 eV

• 3.4 eV

• 6.8 eV

The fraction of atoms of radioactive element that decays in 6 days is 7 / 8. The fraction that decays in 10 days will be

• 77 / 80

• 71 / 80

• 31 / 32 

• 15 / 16

In β⁺ decay process, which of the following changes takes place inside the nucleus

• ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X} \to {}_{\mathrm{Z}+1}{}^{\mathrm{A}}\mathrm{Y} + {\mathrm{e}}^{+} + \mathrm{v}$

• ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X} \to {}_{\mathrm{Z}+1}{}^{\mathrm{A}}\mathrm{Y} + {\mathrm{e}}^{-} + \stackrel{-}{\mathrm{v}}$

• ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X} \to {}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{Y} + {\mathrm{e}}^{-} + \mathrm{v}$

• ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X} \to {}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{Y} + {\mathrm{e}}^{-} + \stackrel{-}{\mathrm{v}}$

The fossil bone has a ¹⁴C : ¹²C ratio which is (1 / 16) of that in a living animal bone. If the half-life time of ¹⁴C is 5730 years, thus the age of the fossil bone is

• 11460 years

• 17190 years

• 22920 years

• 45840 years