The coordination number of $Cu$ is

Which of the following is most unstable?

If the nuclear force between two protons,two neutrons,and between a proton and a neutron is denoted by $F_{pp}$,$F_{nn}$,and $F_{pn}$ respectively,then:

Given below are three schematic graphs of potential energy $V(r)$ versus distance $r$ for three atomic particles: electron $(e^{-})$,proton $(p^{+})$,and neutron $(n)$,in the presence of a nucleus at the origin $O$. The radius of the nucleus is $r_0$. The scale on the $V$-axis may not be the same for all figures. The correct pairing of each graph with the corresponding atomic particle is

The ratio of mass densities of nuclei of $^{40}Ca$ and $^{16}O$ is close to

The mass of a neutron is approximately the same as that of: