The solids that are electrical conductors, malleable and ductile are:

Metallic solids

The correct answer is option 3. Metallic solids.

Here is an explanation of the properties of different types of solids and why metallic solids fit the description of being electrical conductors, malleable, and ductile:

1. Molecular Solids

Molecular solids are composed of discrete molecules held together by weak intermolecular forces such as van der Waals forces, hydrogen bonds, or dipole-dipole interactions.

Properties:

Electrical Conductivity: Molecular solids generally do not conduct electricity because there are no free-moving charged particles (electrons or ions) within the solid.

Malleability and Ductility: Molecular solids are usually brittle and not malleable or ductile. They tend to break or shatter rather than deform.

Examples: Ice (solid water), sugar (sucrose), and dry ice (solid CO₂).

2. Ionic Solids

Ionic solids consist of a regular lattice of positive and negative ions held together by strong electrostatic forces (ionic bonds).

Properties:

Electrical Conductivity: Ionic solids do not conduct electricity in the solid state because the ions are fixed in place within the lattice. However, when melted (molten state) or dissolved in water (aqueous solution), the ions become free to move and thus conduct electricity.

Malleability and Ductility: Ionic solids are typically brittle. When stress is applied, the lattice structure can shift, causing like-charged ions to align and repel each other, leading to fracture rather than deformation.

Examples: Sodium chloride (NaCl), magnesium oxide (MgO).

3. Metallic Solids

Metallic solids consist of metal atoms arranged in a regular lattice structure. The atoms are surrounded by a "sea" of delocalized (free-moving) electrons that are not bound to any specific atom.

Properties:

Electrical Conductivity: Metallic solids are excellent conductors of electricity because the delocalized electrons are free to move throughout the lattice, allowing them to carry electric current.

Malleability and Ductility: Metallic solids are both malleable and ductile. The layers of metal atoms can slide past one another without breaking the metallic bonds because of the non-directional nature of the metallic bonds. This allows metals to be hammered into thin sheets (malleability) or drawn into wires (ductility).

Examples: Copper, aluminum, gold.

4. Covalent Solids

Covalent solids (also known as network solids) are made up of atoms connected by a continuous network of covalent bonds, forming a three-dimensional lattice.

Properties:

Electrical Conductivity: Covalent solids typically do not conduct electricity because there are no free-moving charged particles. All the electrons are involved in covalent bonding and are not free to miove.

Malleability and Ductility: Covalent solids are generally hard and brittle. They lack the ability to deform easily without breaking the covalent bonds, so they are not malleable or ductile.

Examples: Diamond, silicon carbide (SiC).

Summary

Metallic solids are unique among the types of solids listed because they possess a lattice of metal atoms surrounded by a sea of delocalized electrons, which accounts for their electrical conductivity, malleability, and ductility. The free-moving electrons allow metallic solids to conduct electricity, while the flexibility of the metallic bond allows them to be shaped and stretched without breaking.