Question

Among the elements $Ca, Mg, P$ and $Cl$, the order of increasing atomic radii is

• A. Mg < Ca < Cl < P
• B. Cl < P < Mg < Ca
• C. P < Cl < Ca < Mg
• D. Ca < Mg < P < Cl

Answer 1

Answer: (B)

Atomic radii increases, as the number of shells increases. Thus, on moving down a group atomic radii increases.
The electronic configuration of the given element is $Mg _{12}=[ Ne ] 3 s ^{2}$
$Ca _{20}=[ Ar ] 4 s ^{2}$
$p _{15}=[ Ne ] 3 s ^{23} p ^{3}$
$Cl _{17}=[ Ne ]_{3} s ^{23} p ^{5}$
On the other hand, on increasing the number of electron in the same shell, the atomic radii decreases because effective nuclear charge is increases. In $Mg , P$ and $C 1$, the number of electrons are increasing in the same shell, thus the order of their atomic radii is
$Cl < P < Mg$
In case of Ca, the electron is entering in higher shell. So, its atomic radii is highest. Thus, the order of radii is
$Cl < P < Mg < Ca$