Assertion : An atom is electrically neutral.
Reason : Atom contains equal number of protons and neutrons.

The atomic configurations of atoms $A$,$B$,and $C$ are given as: $A = [Z(90) + n(146)]$,$B = [Z(92) + n(146)]$,$C = [Z(90) + n(148)]$. Which of the following statements are incorrect?
$(a) A$ and $C$ are isotones.
$(b) A$ and $C$ are isotopes.
$(c) A$ and $B$ are isobars.
$(d) B$ and $C$ are isobars.
$(e) B$ and $C$ are isotopes.

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

Give the symbol of the following species:
$(i)$ Number of electrons,protons,and neutrons are $10, 8$,and $8$ respectively.
$(ii)$ $Ca$ $(Z = 20)$ and nucleon number $= 40$.
$(iii)$ Species with mass number $25$,protons $12$ (magnesium),and electrons $10$.
$(iv)$ Species of Bromine in which $(Z = 35)$,electrons $36$,and neutrons $45$.
$(v)$ $+2$ positive and $-2$ negative ions that are isoelectronic with $Al^{3+}$ $(Z = 13)$.

Atomic number means

$_{18}Ar^{40}$,$_{20}Ca^{40}$ and $_{19}K^{40}$ are