### JEE Mains Previous Years Questions with Solutions

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1

### 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.
2

### 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
3

### 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
4

### AIEEE 2011

Outer electronic configuration of Gd (Atomic no : 64) is -
A
4f85d06s2
B
4f45d46s2
C
4f75d16s2
D
4f35d56s2

## Explanation

Electronic configuration of Gd(64) : [Xe]4f75s25p65d16s2

So the outer electronic configuration will be : 4f75d16s2

Shortcut Method : Gd belongs to 4f series which is also called lanthanide series. In this lanthanide series for Cerium (Ce), Gadolinium (Gd) and Lutetium (Lu) outer d orbital has 1 electron and for all other lanthanide series elements outer d orbital has 0 electron. From this you can easily say option (C) is correct.