Question

Which of the following orders of ionic radii is correctly represented?
A. `H^(-) gt H^(+) gt H`
B. `Na^(+) gt F^(-) gt O^(2-)`
C. `F^(-) gt O^(2-) gt Na^(+)`
D. `Al^(3+) gt Mg^(2+) gt N^(3-)`

Answer 1

Correct Answer - A
All the option (b,c and d) are incorrect .
(a) `H^(-)gtHgtH^(+)`
It is known that radius of a cation is always smaller than that of a neutral atom due to decrease in the number of orbits. Whereas the radius of anion is always greater than a cation due to decrease in effective nuclear charge. Hence the correct order is `H^(-) gt H gt H^(+)`.
(b) `Na^(+) gt F^(-) gt O^(2-)`
the given species are isoelectronic and they are in contact with the same number of electrons. For isoelectronic species.
Ionic radii `prop 1/("atomic number")`
`:.` The correct order of ionic radii is `O^(2-) gt F^(-) gt Na^(+)`
(c ) Similarly, the correct option is `O^(2-) gt F^(-) gt Na^(+)`
(d) The correct order is `N^(3-) gt Mg^(2+) gt Al^(3+)`.