Question

In which of the following the s-block elements are arranged in the correct order of their melting points?

• A. \(\text{Mg}>\text{Be}>\text{Na}>\text{Li}\)
• B. \(\text{Li}>\text{Be}>\text{Mg}>\text{Na}\)
• C. \(\text{Be}>\text{Mg}>\text{Li}>\text{Na}\)
• D. \(\text{Li}>\text{Mg}>\text{Na}>\text{Be}\)

Hint:

Be has the highest melting point among s-block elements due to its small size and strong metallic lattice. Mg has an exceptionally low melting point for Group 2 due to its hexagonal close packing structure.

Answer 1

The Correct Option is C

Step 1: Trends in Melting Points:
* Group 2 vs Group 1: Group 2 elements (Alkaline earth metals) generally have higher melting points than Group 1 elements (Alkali metals) due to smaller atomic size and two valence electrons contributing to stronger metallic bonding. So, Be and Mg will have higher MPs than Li and Na. * Group 2 Trend: Melting points generally decrease down the group, but there are irregularities. Be has a very high MP (\(1287^\circ\text{C}\)). Mg (\(650^\circ\text{C}\)) is lower than Ca, but definitely lower than Be. * Group 1 Trend: Melting points decrease down the group as metallic bond strength weakens with increasing size. Li (\(180^\circ\text{C}\))>Na (\(98^\circ\text{C}\)).
Step 2: Comparison:
* \(\text{Be} \approx 1560 \text{ K}\) * \(\text{Mg} \approx 924 \text{ K}\) * \(\text{Li} \approx 454 \text{ K}\) * \(\text{Na} \approx 371 \text{ K}\) Order:
\(\text{Be}>\text{Mg}>\text{Li}>\text{Na}\). Final Answer:
Option (C).