The nucleus of helium contains

The electronic configuration of a dipositive metal $M^{2+}$ is $2, 8, 14$ and its atomic weight is $56 \ a.m.u.$ The number of neutrons in its nuclei would be

How is an atom represented using notation? Provide an example.

Match the following atomic species with their correct classification:

$(i) \ { }_{26} Fe ^{54}, { }_{26} Fe ^{56}, { }_{26} Fe ^{57}, { }_{26} Fe ^{58}$	$(a)$ Isotopes
$(ii) \ { }_1 H ^3, { }_2 He ^3$	$(b)$ Isotones
$(iii) \ { }_{32} Ge ^{76}, { }_{33} As ^{77}$	$(c)$ Isodiaphers
$(iv) \ { }_{92} U ^{235}, { }_{90} Th ^{231}$	$(d)$ Isobars
$(v) \ { }_1 H ^1, { }_1 D ^2, { }_1 T^3$

Two atoms of elements $X$ and $Y$ are isotones of each other. Their mass numbers are $70$ and $72$ respectively. If the atomic number of $X$ is $34$,then the atomic number of $Y$ is ..........

The nitrogen atom has $7$ protons and $7$ electrons. The nitride ion $(N^{3-})$ will have: