1

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.
2

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
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 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