In medicine,to destroy cancer cells . . . . . . rays are used.

$A$ radioactive nucleus decays as follows. If the atomic number of $X$ is $72$ and the mass number is $180$,what are the mass number and atomic number of $X_4$?
$X \xrightarrow{\alpha} X_1 \xrightarrow{\beta} X_2 \xrightarrow{\alpha} X_3 \xrightarrow{\gamma} X_4$

$A$ certain radioactive nuclide of mass number $m_x$ disintegrates,with the emission of an electron and $\gamma$ radiation only,to give a second nuclide of mass number $m_y$. Which one of the following equations correctly relates $m_x$ and $m_y$?

In the following nuclear reaction,$D \xrightarrow{\alpha} D_{1} \xrightarrow{\beta^-} D_{2} \xrightarrow{\alpha} D_{3} \xrightarrow{\gamma} D_{4}$. The mass number of $D$ is $182$ and the atomic number is $74$. The mass number and atomic number of $D_{4}$ respectively will be:

$A$ radioactive nucleus undergoes $\alpha$-emission to form a stable element. What will be the recoil velocity of the daughter nucleus if $V$ is the velocity of $\alpha$-emission and $A$ is the atomic mass of the radioactive nucleus?

Assertion: ${}^{90}Sr$ from the radioactive fallout of a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells.
Reason: The energetic $\beta$-particles emitted in the decay of ${}^{90}Sr$ damage the bone marrow.