An atom having atomic mass number $13$ has $7$ neutrons. What is the atomic number of the atom?

If the mass attributed to a neutron were halved and that attributed to the electron were doubled,the atomic mass of $_6C^{12}$ would

If the electronic configuration of a metal ion $M^{2+}$ is $2, 8, 14$ and its atomic mass is $56 \, a.m.u.$,then the number of neutrons in its nucleus is .....

Calculate the number of protons,neutrons and electrons in $_{35}^{80}Br$.

When a sulphur atom becomes a sulphide ion,

The spectrum of Helium is expected to be similar to that of . . . . . .