NEET Solved Paper 2014 Question 16
Question: Which of the following orders of ionic radii is correctly represented? [AIPMT 2014]
Options:
A) $ {H^{-}}>,{H^{+}}>H $
B) $ N{a^{+}}>{F^{-}}>{O^{2-}} $
C) $ {F^{-}}>{O^{2-}}>N{a^{+}} $
D) None of these
Show Answer
Answer:
Correct Answer: D
Solution:
- (No option is correct)
[a] $ {H^{-}}>{H^{+}}>H $ 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^{-}}>H>{H^{+}} $
[b] $ N{a^{+}}>{F^{-}}>{O^{2-}} $ The given species are isoelectronic as they contain same number of electrons. For isoelectronic species, $ ionicradii\propto \frac{1}{atomicnumber} $ Ion: $ N{a^{+}}{F^{-}}{O^{2-}} $ Atomic number: 11 9 8 Hence, the correct order of ionic radii is $ {O^{2-}}>{F^{-}}>N{a^{+}} $
[c] Similarly, the correct option is $ {O^{2-}}>{F^{-}},>N{a^{+}}, $ [d] Ion : $ A{l^{3+}} $ $ M{g^{2+}} $ $ {N^{3-}} $
Atomic number: 13 12 7 Hence, the correct order is $ {N^{3-}},>M{g^{2+}},>A{l^{3+}} $ .
