Structure of Atoms and Nuclei

'Half-life' of a radioactive substance accounts for

According to the Bohr's atomic model, the relation between principle quantum number $(n)$ and radius of orbit ( $r$ ) is

A nuclear reaction given by ${}_{Z}X^{A}\rightarrow{}_{Z+1}Y^{A}+{}_{-1}e^{0}+\bar{v}$ represents

The radius of electron's second stationary orbit in Bohr's atom is R. The radius of the third orbit will be

Alpha-particles that come closer to nuclei

Which of the following is an integral multiple of $\dfrac{h}{2 \pi}$ in Bohr's model of an hydrogen atom?

When a uranium isotope ${}_{92}^{235}U$ is bombarded with a neutron, it generates ${}_{36}^{89}Kr$, three neutrons and

In Bohr's model of hydrogen atom, which of the following pairs of quantities are quantized?

If $N_{0}$ is the original mass of the substance of half life period 5 years, then the amount of substance left after 15 years is

In the hydrogen atom, radii of the first four Bohr orbits are related as

The half-life of the isotope ${ }_{11} \mathrm{Na}^{24}$ is 15 hr. How much time does it take for $\left(\dfrac{7}{8}\right)^{\text {th }}$ of a sample of this isotope to decay ?

The angular momentum of the electron in the third Bohr orbit of a hydrogen atom is ' $l$ ' so its angular momentum in the fourth Bohr orbit is

A radioactive sample has half-life of 5 years. The percentage of fraction decayed in 10 years will be

If the ionisation energy for the hydrogen atom is 13.6 eV, then the energy required to excite it from the ground state to the next higher state is nearly

A radioactive element having half-life 30 min . is undergoing beta decay. The fraction of radioactive element remains undecayed after 90 min . will be