1

### 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
2

### 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.
3

### AIPMT 2010 Mains

Among the following which one has the highest cation to anion size ratio ?
A
CsI
B
CsF
C
LiF
D
NaF

## Explanation

The ratio in cation and anion size will be maximum when the cation is largest size and the anion is smallest size. So among the given species, Cs+ has maximum size among given cations and F- has smallest size among the given anions, So Cs/F has highest rc/ra
4

### AIPMT 2010 Prelims

Which of the following represents the correct order of increasing electron gain enthalpy with negative sign for the elements O, S, F and C$l$ ?
A
C$l$ < F < O < S
B
O < S < F < C$l$
C
F < S < O < C$l$
D
S < O < C$l$ < F

## Explanation

Cl atom has the highest electron affinity in the periodic table. F is a member of group 17 has highest electron gain enthalpy than S which is a group 16 element. This is turn is higher than the electron affinity of O atom. Thus,

Cl > F > S > O