If the mass number of an atom is $A = 40$ and its electron configuration is $1s^2, 2s^2, 2p^6, 3s^2, 3p^6$,the number of neutrons and protons in its nucleus will be

$A$ nucleus at rest splits into two nuclear parts having radii in the ratio $1:2$. Their velocities are in the ratio: (in $:1$)

Which of the following pairs of nuclei represents isotones?

Briefly explain the discovery of neutrons and how it can be demonstrated.

If the nucleus ${}_{13}^{27}Al$ has a nuclear radius of about $3.6 \, fm$,then ${}_{52}^{125}Te$ would have its radius approximately as .......$fm$.

The three stable isotopes of neon: $_{10}^{20}Ne$,$_{10}^{21}Ne$,and $_{10}^{22}Ne$ have respective abundances of $90.51\%$,$0.27\%$,and $9.22\%$. The atomic masses of the three isotopes are $19.99\;u$,$20.99\;u$,and $21.99\;u$ respectively. Obtain the average atomic mass of neon. (in $;u$)