# Which arrangement is in the correct order of radius size? a) Mn > Mn2+ > Cs b) Li+ > Li > Ra c) P < P3– < As3– d) Cr < Cr3+ < Ca e) Al3+ > Al > Si

Apr 11, 2015

The answer is c) $P < {P}^{3 -} < A {s}^{3 -}$

According to the periodic trend in atomic size, radius size increases when going down a group and decreases when going from left to right across a period.

When it comes to ionic size, cations are smaller than their neutral atoms, while anions are larger than their neutral atoms.

Using these guidelines you can easily maneuver through the options given to you.

Option a) is eliminated because cesium is a massive atom when compared with neutral manganese - the former is located two periods further down the periodic table than the latter (period 6 vs. period 4).

Option b) is eliminated because the lithium cation, $L {i}^{+}$, is not bigger than the neutral lithium atom. Moreover, radium is the largest of the three, not the smallest.

Option c) is correct because the neutral phosphorus atom is smaller than the phosphorus anion, ${P}^{3 -}$, which in turn will be smaller than the arsenic anion, $A {s}^{3 -}$, because arsenic is located down the group from phosphorus.

Option d) is incorrect because the cromium atom is not smaller than the $C {r}^{3 +}$ cation. Moreover, the calcium atom, being located further to the left of cromium, is the largest of the three.

Option e) is eliminated because the aluminium atom cation, $A {l}^{3 +}$, is not larger than the neutral aluminium atom.