Question

Identify the elements $X$ and $Y$ using the ionisation energy values given below :

	1st Ionisation Enthalpy(KJ/mol)	2nd Ionisation Enthalpy(KJ/mol)
$X$	$495$	$4563$
$Y$	$731$	$1450$

• A. $X=Na;Y=Mg$
• B. $X=Mg;Y=F$
• C. $X=F;Y=Mg$
• D. $X=Mg;Y=Na$

Answer 1

The correct option is A $X=Na;Y=Mg$

Due to $2p^6$, noble gas electronic configuration, the second ionisation enthalpy of $Na$ is very high. That's why has large difference between $I{E}_1\text{and}I{E}_2$ of $M{g}^{+}\text{is}2p^6,3s^1.$
After the loss of one electron, $M{g}^{2+}$ will be formed with noble gas electronic configuration. That's why it has less difference between $I{E}_1\text{and}I{E}_2.$
Thus option (a) is the correct answer.