1

### AIPMT 2009

Amongst the elements with following electronic configurations, which one of them may have the highest ionisation energy ?
A
Ne [3s2 3p2]
B
Ar [3d10 4s2 4p3]
C
Ne [3s2 3p1]
D
Ne [3s2 3p3]

## Explanation

Among the given options (a), (c) and (d), the option (d) has the highest ionisation energy because of extra stability associated with half-filled 3p-orbital. In option (b), the presence of 3d10 electrons offers shielding effect, as a result the 4p3 electrons do not experience much nuclear charge and hence the electrons can be removed easily.
2

### AIPMT 2007

With which of the following electronic configuration an atom has the lowest ionisation enthalpy ?
A
1s2 2s2 2p3
B
1s2 2s2 2p5 3s1
C
1s2 2s2 2p6
D
1s2 2s2 2p5

## Explanation

The larger the atomic size, smaller is the value of the ionisation enthalpy. Again higher the screening effect, lesser is the value of ionisation potential, So option(b) has lowest ionisation enthalpy.
3

### AIPMT 2007

Identify the correct order of the size of the following :
A
Ca2+ < K+ < Ar < Cl$-$ < S2$-$
B
Ar < Ca2+ < K+ < Cl$-$ < S2$-$
C
Ca2+ < Ar < K+ < Cl$-$ < S2$-$
D
Ca2+ < K+ < Ar < S2$-$ < Cl$-$

## Explanation

Among isoelectronic ions, ionic radius of anions is more than that of cations. Further size of the anion increases with increase in negative charge and size of the cation decreases with increase in positive charge.
4

### AIPMT 2007

Which one of the following ionic species has the greatest proton affinity to form stable compound ?
A
NH$_2^ -$
B
F$-$
C
I$-$
D
HS$-$

## Explanation

Going from left to right across a period in the periodic table, the basicity decreases as the electronegativity of the atom possessing the lone pair of electron increases. Hence basicity of $NH_2^-$ is higher than F-. In moving down a group, as the atomic mass increases, basicity decreases. Hence F- is more basic than I- and HO- is more basic than HS-. Hence among the ionic species, $NH_2^-$ has maximum proton affinity.