The charge on the atom containing $17$ protons,$18$ neutrons and $18$ electrons is

The number of electrons in $Cl^{-}$ ion is

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

$Ca$ has atomic number $20$ and atomic weight $40$. Which of the following statements is not correct about $Ca$ atom?

The group having isoelectronic species is:

The number of protons,electrons and neutrons in a species are equal to $17$,$18$ and $18$ respectively. Which of the following will be the proper symbol of this species?