modern physics Questions

Which of the following cannot be emitted by radioactive substance during their decay?

Which of the following atoms has the lowest ionization potential?

When ${}^{238}\text{U}$ nucleus originally at rest, decays by emitting an alpha particle having a speed $u$, the recoil speed of the residual nucleus is:

In the nuclear fusion reaction ${}_1^2\text{H}{+}_1^3\text{H}{\to }_2^4\text{He}+\text{n}$, given that the repulsive potential energy between the two nuclei is $7.7\times 10^{-14}\text{J}$, the temperature at which the gases must be heated to initiate the reaction is nearly: (Boltzmann’s constant $k=1.38\times 10^{-23}\text{J/K}$)

Two identical photo cathodes receive light of frequencies $f_1$ and $f_2$. If the velocities of the photoelectrons (of mass $m$) coming out are respectively $v_1$ and $v_2$, then:

A nucleus with $Z=92$ emits the following in a sequence: $\alpha ,\alpha ,{\beta }^{-},{\beta }^{-},\alpha ,\alpha ,\alpha ,\alpha ,{\beta }^{-},{\beta }^{-},\alpha ,{\beta }^{+},{\beta }^{+},\alpha$. The $Z$ of the resulting nucleus is:

If the binding energy of the electron in a hydrogen atom is $13.6\text{eV}$, the energy required to remove the electron from the first excited state of ${\text{Li}}^{++}$ is:

The wavelengths involved in the spectrum of deuterium (${}_1^2\text{D}$) are slightly different from that of hydrogen spectrum, because:

Which of the following radiations has the least wavelength?

A radioactive sample at any instant has its disintegration rate $5000\text{disintegrations per minute}$. After $5\text{minutes}$, the rate is $1250\text{disintegrations per minute}$. Then, the decay constant (per minute) is: