The correct answer is D. Silver, Copper, Aluminium, Steel.
Conductivity is the ability of a material to allow the flow of electricity. Materials with high conductivity are good conductors of electricity, while materials with low conductivity are poor conductors of electricity.
The four materials in the question are copper, aluminium, steel, and silver. Copper is the best conductor of electricity, followed by silver, aluminium, and steel. Therefore, the correct order of decreasing conductivity is D. Silver, Copper, Aluminium, Steel.
Here is a table showing the conductivity of the four materials:
| Material | Conductivity (Siemens per meter) |
|—|—|
| Silver | 62.5 x 10^6 |
| Copper | 58.5 x 10^6 |
| Aluminium | 36.8 x 10^6 |
| Steel | 10^6 |
As you can see, silver has the highest conductivity, followed by copper, aluminium, and steel.