An isobar of ${ }_{20} Ca^{40}$ is

Give the relation between the following pairs of species:
$(i)$ $_{20}^{40}Ca$ and $_{19}^{40}K$
$(ii)$ $_{17}^{35}Cl$ and $_{17}^{37}Cl$
$(iii)$ $_{18}^{40}Ar$,$_{20}^{40}Ca$ and $_{19}^{40}K$
$(iv)$ $_{38}^{87}Sr$ and $_{38}^{90}Sr$

The number of protons,neutrons and electrons in ${ }_{71}^{175} Lu$,respectively,are:

Match the following columns:

$(i) \ _{26}Fe^{54}, \ _{26}Fe^{56}, \ _{26}Fe^{58}$	$(a) \ \text{Isotopes}$
$(ii) \ _1H^3, \ _2He^3$	$(b) \ \text{Isotones}$
$(iii) \ _{32}Ge^{76}, \ _{33}As^{77}$	$(c) \ \text{Isoelectronic}$
$(iv) \ _{92}U^{235}, \ _{90}Th^{231}$	$(d) \ \text{Isobars}$
$(v) \ _1H^1, \ _1D^2, \ _1T^3$

Which character is different for the two isotopes of an element?

What are nucleons?