### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2011

Which one of the following order represents the correct sequence of the increasing basic nature of the given oxides ?
A
MgO < K2O < Al2O3 < Na2O
B
Al2O3 < MgO < Na2O < K2O
C
Na2O < K2O < MgO < Al2O3
D
K2O < Na2O < Al2O3 < MgO

## Explanation

You should know that,

(1)$\,\,\,$ In a period, from left to right the acidic strength increases that mean basic nature decreases.

(2)$\,\,\,$ In a group, from top to bottom the basic nature increases that means acidic nature decreases.

Na, Mg, Al and K are present in periodic table like this : -

Group 1 Group 2 Group 13
Period 3 Na Mg ..... Al
Period 4 K

So, you can see Na, Mg and Al are present in same period so the order of basic nature among Na, Mg and Al is Na > Mg > Al.

And Na and K are from same group so basic nature of K > Na.

So the correct order of oxides

Al2O3 < MgO < Na2O < K2O
2

### AIEEE 2010

The correct sequence which shows decreasing order of the ionic radii of the elements is
A
Al3+ > Mg2+ > Na+ > F- > O2-
B
Na+ > Mg2+ > Al3+ > O2– > F
C
Na+ > F > Mg2+ > O2– > Al3+
D
O2– > F > Na+ > Mg2+ > Al3+

## Explanation

As you can see all of them are isoelectronic and for isoelectric elements which ion has more positive charge will have lesser size. And which ion has more negative charge that ion's size will be more.

So, the correct order is

${O^{2 - }} > {F^ - } > N{a^ + } > m{g^{2 + }} > A{l^{3 + }}$
3

### AIEEE 2009

The set representing the correct order of ionic radius is :
A
$N{a^ + } > L{i^ + } > M{g^{2 + }} > B{e^{2 + }}$
B
$L{i^ + } > N{a^ + } > M{g^{2 + }} > B{e^{2 + }}$
C
$M{g^{2 + }} > B{e^{2 + }} > L{i^ + } > N{a^ + }$
D
$L{i^ + } > B{e^{2 + }} > N{a^ + } > M{g^{2 + }}$

## Explanation

In periodic table $Li, Na, Mg, Be$ are present in following ways :-

Group  1 Group  2
Li Be
Na Mg

Note :

$(1)\,\,\,$ In periodic table from left to right the size of element decreases.

$(2)\,\,\,$ In periodic table, from top to bottom size of element increases.

So, $B{e^{ + 2}}$ will be the smallest in size.

Among $L{i^ + }$ and $N{a^ + },$ size of $N{a^ + } > L{i^ + }$ and among $B{e^{ + 2}}$ and $M{g^{ + 2}},$ size of $M{g^{ + 2}} > B{e^{ + 2}}$.

Note : Size of $L{i^ + } > M{g^{ + 2}},$ this is a exception case.

So, the correct order will be, $N{a^ + } > L{i^ + } > M{g^{ + 2}} > B{e^{ + 2}}$
4

### AIEEE 2009

In which of the following arrangements, the sequence is not strictly according to the property written against it?
A
CO2 < SiO2 < SnO2 < PbO2 : increasing oxidising power
B
HF< HCl < HBr < HI : increasing acid strength
C
NH3 < PH3 < AsH3 < SbH3 : increasing basic strength
D
B < C < O < N : increasing first ionization enthalpy