### JEE Mains Previous Years Questions with Solutions

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1

### JEE Main 2015 (Offline)

The ionic radii (in Å) of N3–, O2– and F are respectively:
A
1.36, 1.71 and 1.40
B
1.71, 1.40 and 1.36
C
1.71, 1.36 and 1.40
D
1.36, 1.40 and 1.71

## Explanation

Here all of them are isoelectric and for isoelectric species size of anion increases as negative charge increases.

So, correct order is :

N3– > O2– > F

$\therefore$ Radius of N3– = 1.71 Å

and Radius of O2– = 1.40 Å

and Radius of F = 1.36 Å
2

### JEE Main 2013 (Offline)

The first ionization potential of Na is 5.1 eV. The value of electron gain enthalpy of Na+ will be:
A
– 5.1 eV
B
–10.2 eV
C
+ 2.55 eV
D
– 2.55 eV

## Explanation

Ionization potential of Na means energy required to convert of Na to Na+ ion.

Na $\to$ Na+ + e-          IE = 5.1 ev

Electron gain enthalpy of Na+ means energy required to convert Na+ ion to Na.

Na $\to$ Na+ + e-          $\Delta {H_{eq}}$ = - 5.1 ev

According to Lavoisier and Laplace law of thermochemistry, when we change the direction of reaction then the sign of energy also changes.
3

### JEE Main 2013 (Offline)

Which of the following represents the correct order of increasing first ionization enthalpy for Ca, Ba, S, Se and Ar?
A
S < Se < Ca < Ba < Ar
B
Ba < Ca < Se < S < Ar
C
Ca < Ba < S < Se < Ar
D
Ca < S < Ba < Se < Ar

## Explanation

Those elements are present in periodic table like this -

Group 2 Group 16 Group 18
Period 3 Ca .......... S ......... Ar
Period 4 Sc
Period 5 Ba

In periodic table,

1. From left to right ionization energy increases.

2. From top to bottom ionization energy decreases.

$\therefore$ Ba < Ca and Se < S and S < Ar

$\therefore$ Correct order is -
Ba < Ca < Sc < S < Ar
4

### AIEEE 2012

The increasing order of the ionic radii of the given isoelectronic species is :
A
Cl, Ca2+ , K+ , S2–
B
S2–, Cl, Ca2+ , K+
C
Ca2+ , K+ , Cl , S2–
D
K+, S2–, Ca2+, Cl