Which ion has the lowest radius from the following ions?

Identify the isoelectronic species from the following groups.

Observe the following data.

Ion	Radius $(pm)$
$Q^{a+}$	$53$
$X^{b+}$	$66$
$Y^{c+}$	$40$
$Z^{d+}$	$100$

$Q^{a+}, X^{b+}, Y^{c+}, Z^{d+}$ are respectively

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$: The ionic radii of $O^{2-}$ and $Mg^{2+}$ are same.
Reason $R$: Both $O^{2-}$ and $Mg^{2+}$ are isoelectronic species.
In the light of the above statements,choose the correct answer from the options given below:

The order of increasing sizes of atomic radii among the elements $O$,$S$,$Se$ and $As$ is

Which of the following sequences is the correct order of the size of species?