Six protons are found in the nucleus of

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 $_{38}^{90}Sr$

An atom has the electronic configuration of $1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^{10}, 4s^2 4p^5$. Its atomic weight is $80$. Its atomic number and the number of neutrons in its nucleus shall be

The specific charge of a proton is $9.6 \times 10^7 \ C \ kg^{-1}$. What will be the specific charge for an $\alpha$-particle?

Elements having different nuclear charge but the same mass number are called

The atomic number of an element is always equal to