Question

Which of the following is the correct order with respect to the property indicated?

• A. Cl>F (Ionisation energy)
• B. K₂O>Na₂O>Al₂O₃ (Basic nature)
• C. K>Na>Mg>Al (Metallic character)
• D. None of these

Hint:

In periodic trends, ionisation energy increases across a period and decreases down a group, while metallic character behaves oppositely.

Answer 1

The Correct Option is B

The question requires us to identify the correct order of substances with respect to the property indicated. Let's evaluate each option to determine the correct answer:

1. Cl > F (Ionisation energy)
   • Ionisation energy generally decreases down a group. However, within a period, it generally increases from left to right. Fluorine (F) typically has higher ionisation energy than chlorine (Cl) because it is smaller in size and holds its electrons more tightly.
   • Thus, the order should be F > Cl, not Cl > F, making this option incorrect.
2. K₂O > Na₂O > Al₂O₃ (Basic nature)
   • Basicity is related to the metallic character and group trend in the periodic table. Metal oxides tend to form basic solutions in water.
   • The basic nature typically increases down a group and decreases across a period from left to right.
   • The order of basicity is generally K₂O > Na₂O > Al₂O₃ because K₂O and Na₂O are strong bases due to their high metallic character compared to Al₂O₃, which is amphoteric.
   • Therefore, this option is correct.
3. K > Na > Mg > Al (Metallic character)
   • Metallic character generally increases down a group and decreases across a period from left to right.
   • Among the given elements (K, Na, Mg, Al), the expected order is Na > Mg > Al, not K > Na > Mg > Al. Thus, this sequence is also incorrect.
4. None of these
   • This option is incorrect because we identified that option (K₂O > Na₂O > Al₂O₃) is indeed correct regarding the basic nature of the compounds.

Consequently, the correct order with respect to basic nature is K₂O > Na₂O > Al₂O₃.