1

### AIPMT 2015 Cancelled Paper

The species Ar, K+ and Ca2+ contain the same number of electrons. In which order do their radii increase ?
A
Ca2+ < K+ < Ar
B
K+ < Ar < Ca2+
C
Ar < K+ < Ca2+
D
Ca2+ < Ar < K+

## Explanation

For isoelectronic species, radius of atom decreases with increase in nuclear charge.
2

### 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+
3

### 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.
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