1

### NEET 2016 Phase 1

In which of the following options the order of arrangement does not agree with the variation of property indicated against it ?
A
I < Br < Cl < F (increasing electron gain enthalpy)
B
Li < Na < K < Rb (increasing metallic radius)
C
Al3+ < Mg2+ < Na+ < F$-$ (increasing ionic size)
D
B < C < N < O (increasing first ionisation enthalpy)

## Explanation

The correct order of increasing negative electron gain enthalpy is : I < Br < F < Cl and the correct order of increasing first ionisation enthalpy is B < C < O < N.
2

### 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.
3

### 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+
4

### 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.