Which of the following is most unstable?

$A$ nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei,the products must move in opposite directions.

The atomic masses of two isotopes of an element are $34.98 \ u$ and $36.98 \ u$ and their relative abundances are $75.4 \%$ and $24.6 \%$ respectively. The average atomic mass of the element is: (in $u$)

Write the unit of mass in nuclear physics and define it and it is equivalent to how many kilograms?

An element consists of a mixture of three isotopes $A$, $B$, and $C$ of masses $m_1$, $m_2$, and $m_3$ respectively. If the relative abundances of the three isotopes $A$, $B$, and $C$ are in the ratio $2:3:5$, the average mass of the element is:

The nuclear radius is given by $R = r_0 A^{1/3}$,where $r_0$ is a constant and $A$ is the atomic mass number. Then,the nuclear mass density of $^{238}U$ is