To order the planets from smallest to largest diameter based on the provided values:
- Mercury: 4.87 x 10^3 kilometers
- Mars: 6.79 x 10^3 kilometers
- Venus: 1.21 x 10^4 kilometers
- Earth: 1.28 x 10^4 kilometers
The correct order from smallest to largest diameter is:
- Mercury
- Mars
- Venus
- Earth