An ion $Y^{3-}$ contains $18$ electrons and $16$ neutrons. Calculate the atomic number and mass number of the element $Y$. Name the element $Y$.

(N/A) The number of electrons in the $Y^{3-}$ ion is $18$.
$A$ negative charge is formed by the gain of electrons by a neutral atom,and the number of electrons gained is equal to the magnitude of the negative charge.
Therefore,the number of electrons in the neutral atom $Y$ is $18 - 3 = 15$.
For a neutral atom,the atomic number is equal to the number of protons,which is also equal to the number of electrons.
Therefore,the atomic number of the element $Y$ is $15$.
The mass number of an element is the sum of the number of protons and the number of neutrons.
Mass number $= 15 + 16 = 31$.
The element $Y$ with atomic number $15$ is Phosphorus $(P)$.