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Chemistry
The correct order of first ionisation enthalpies of the following elements is
Q. The correct order of first ionisation enthalpies of the following elements is
2084
178
KEAM
KEAM 2015
The s-Block Elements
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A
B
e
>
M
g
>
C
a
>
S
r
>
R
a
>
B
a
50%
B
R
a
>
B
a
>
S
r
>
C
a
>
M
g
>
B
e
0%
C
B
e
>
M
g
>
C
a
>
S
r
>
B
a
>
R
a
25%
D
R
a
>
S
r
>
B
a
>
M
g
>
C
a
>
B
e
0%
E
B
e
>
M
g
>
C
a
>
R
a
>
B
a
>
S
r
0%
Solution:
Ionisation enthalpy decrease on going down the group.
So,
I
E
∝
size
1
However, radium has exceptionally higher ionisation enthalpy in group
2.
The first ionisation enthalpy in kJ
m
o
l
−
1
of alkali metal and alkaline earth metals are as following:
B
e
=
899
;
M
g
=
737
C
a
=
590
;
S
r
=
549
R
a
=
509
;
B
a
=
503
Hence, order of ionisation enthalpy is
B
e
>
M
g
>
C
a
>
S
r
>
R
a
>
B
a