Question

The second ionisation enthalpy of which of the following alkaline earth metals is the highest?

• A. $Ba$
• B. $Mg$
• C. $Ca$
• D. $Sr$
• E. $Be$

Answer 1

Answer: (E)

$Be$

As all members of the given options belong to the same group, therefore, size will decide the amount of 2nd ionisation energy.
$\because IE\propto \frac{1}{Size}$
Thus, smaller is the size, more is the ionisation energy.
Therefore, $Be$ has highest second ionisation enthalpy.