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1

### 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.
2

### 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
3

### 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

4

### AIPMT 2010 Prelims

The correct orfer of the decreasing ionic radii among the following isoelectronic species is
A
Ca2+ > K+ > S2$$-$$ > C$$l$$$$-$$
B
C$$l$$$$-$$ > S2$$-$$ > Ca2+ > K+
C
S2$$-$$ > Cl$$-$$ > K+ > Ca2+
D
K+ > Ca2+ > Cl$$-$$ > S2$$-$$

## Explanation

For isoelectronic species, ionic radius increases when there is increase in negative charge. It happens because effective nuclear charge on the atom (Zeff) decreases.

Same when ionic radius decreases with increase in positive charge as Zeff increases.

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