Number of electrons in sodium ion$\left({\mathrm{Na}}^{+}\right)$ and oxide ion$\left({\mathrm{O}}^{2-}\right)$ are

Neutrons are present in all elements except

An atom of an element has $15$ electrons and has a mass number $31$. The nucleus of this atom contains _____ neutrons.

Who measured the e/m value of electron?

$\mathrm{C}-14$ has a half-life period of _____

Which species of phosphorus is the most stable?

How many electrons are present in the outermost shell of aluminium?