Question

The first ionization energy of magnesium is smaller as compared to that of elements X and Y, but higher than that of Z. The elements X, Y and Z, respectively, are :

• A. argon, chlorine and sodium
• B. chlorine, lithium and sodium
• C. argon, lithium and sodium
• D. neon, sodium and chlorine

Hint:

Noble gases always have the highest \(IE\) in their respective periods due to their octet stability.

Answer 1

The Correct Option is A

Step 1: Recall the trend of First Ionization Energy (\(IE_1\)) in the 3rd period: \[Na<Al<Mg<Si<S<P<Cl<Ar\] (Note: \(Mg>Al\) and \(P>S\) due to stable electronic configurations).
Step 2: Magnesium's \(IE_1\) is lower than Chlorine (X) and Argon (Y), but higher than Sodium (Z).
Step 3: Checking Option (A): \(Mg\) (737 kJ/mol) is indeed less than \(Cl\) (1251 kJ/mol) and \(Ar\) (1520 kJ/mol), and greater than \(Na\) (496 kJ/mol).