1

### AIPMT 2014

Which of the following orders of ionic radii is correctly represented ?
A
H$-$ > H$^ \bullet$ > H+
B
Na+ > F$-$ > O2$-$
C
F$-$ > O2$-$ > Na+
D
A$l$3+ > Mg2+ > N3$-$

## Explanation

Cation loose electrons are smaller in size than the parent atom, where anions gain electrons are larger in size than the parent atom.

Hence the order is H- > H > H+
2

### NEET 2013 (Karnataka)

Which one of the following arrangements represents the correct order of least negative to most negative electron gain enthalpy for C, Ca, Al, F and O?
A
A$l$ < Ca < O < C < F
B
A$l$ < O < C < Ca < F
C
C < F < O < A$l$ < Ca
D
Ca < A$l$ < C < O < F

## Explanation

Electron gain enthalpy becomes less negative from top to bottom in a group while it becomes more negative from left to right within a period.
3

### AIPMT 2012 Prelims

Identify the wrong statement in the following.
A
Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius.
B
Amongst isoelectronic species, greater the negative charge on the anion, larger is the ionic radius.
C
Atomic radius of the elements increases as one moves down the first group of the periodic table.
D
Atomic radius of the elements decreases as one moves across from left to right in the 2nd period of the periodic table.

## Explanation

When positive charge on the cation increases, effective nuclear charge increases. Thus atomic size decreases.
4

### AIPMT 2011 Mains

What is the value of electron gain enthalpy of Na+ if IE1 of Na = 5.1 eV?
A
$-$ 5.1 eV
B
$-$ 10.2 eV
C
+2.55 eV
D
+10.2 eV

## Explanation

Na $\to$ Na+ + e-; $\Delta$H = 5.1 eV

Na+ + e- $\to$ Na; $\Delta$H = -5.1 eV