Assertion: Covalent solids have highest melting point.

Reason: Covalent solids contains covalently bonded atoms in 3D cross ntwork.

Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

The correct answer is option 1. Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

Assertion: Covalent solids have the highest melting point.

Covalent solids, or network solids, are materials where atoms are bonded by covalent bonds in a continuous 3D network. These bonds are very strong and require a significant amount of energy to break. Examples:

Diamond: Each carbon atom is tetrahedrally bonded to four other carbon atoms, forming an extremely strong and rigid structure.

Quartz \((SiO_2)\): Each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement, forming a rigid 3D network.

Due to the extensive network of strong covalent bonds, covalent solids typically have very high melting points. The melting point of diamond, for example, is about 3550°C, and quartz melts at around 1670°C. The energy required to break these bonds and convert the solid into a liquid phase is exceptionally high, contributing to their high melting points.

Reason: Covalent solids contain covalently bonded atoms in a 3D network.

The 3D network of covalent bonds in these solids creates a highly stable structure. Each atom is covalently bonded to multiple neighboring atoms, forming a continuous and extensive network. This 3D bonding contributes significantly to the physical properties of covalent solids, including hardness, rigidity, and high melting points. To melt a covalent solid, you need to supply enough energy to break numerous strong covalent bonds throughout the material. This is in contrast to other types of solids, such as molecular solids (held together by weaker van der Waals forces) or ionic solids (where ionic bonds can be strong, but not as strong as the covalent bonds in network solids).

Conclusion

Assertion: Covalent solids have the highest melting point. This is  correct as covalent network solids like diamond and quartz have very high melting points due to the strength of the covalent bonds.

Reason: Covalent solids contain covalently bonded atoms in a 3D network. This is a correct statement and accurately explains why covalent solids have high melting points. The extensive 3D covalent bonding network requires significant energy to break, leading to high melting points.