| Elements 1st | Lionization 2nd | Enthalpy (KJ/mol) | |
| A | 899 | 1757 | 14847 |
| B | 737 | 1450 | 7731 |
A) Both 'A' and 'B' belong to group-1 where 'B' comes below 'A'.
B) Both 'A' and 'B' belong to group-1 where 'A' comes below 'B.
C) Both 'A' and 'B' belong to group-2 where 'B' comes below 'A'.
D) Both 'A' and 'B' belong to group-2 where 'A' comes below 'B'.
Correct Answer: C
Solution :
[c] Generally, the ionization enthalpies or energy increases from left to right in a period and decreases from top to bottom in a group. Several factor such as atomic radius, nuclear charge, shielding effect are responsible for change of ionization enthalpies. Here, 1st ionization enthalpy of A and B is greater than group-1 (\[Li=520\text{ }kJmo{{l}^{-1}}\] to \[Cs=374\text{ }kJmo{{l}^{-1}}\]), which means element A and B belong to group-2 and all three given ionization enthalpy values are less for element B means B will come below A.
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