In the equation ${ }_{13}^{27} Al + { }_2^4 He \longrightarrow { }_{15}^{30} P + X$,the correct symbol for $X$ is:

The neutron was discovered by

An unstable heavy nucleus at rest breaks into two nuclei which move away with velocities in the ratio of $8:27$. The ratio of the radii of the nuclei (assumed to be spherical) is

Out of gravitational,electromagnetic,Van der Waals,electrostatic,and nuclear forces,which two are able to provide an attractive force between two neutrons?

For a nucleus to be stable,the correct relation between neutron number $N$ and proton number $Z$ is

If the radius of a nucleus with atomic number $Z = 50$ is $9 \times 10^{-15} \ m$,what is the electric potential at its surface?