1. One millimeter is equal to 0.000001 kilometers. This conversion is arrived at by dividing one meter by 1000 (since 1 meter equals 0.001 kilometers) and then further dividing by 1000, as 1 millimeter is equivalent to 0.001 meters.2. One millimeter is also expressed as 1x10^-6 kilometers in scientific notation. This method uses a power of 10 to indicate how many places the decimal point should be moved to the left, with -6 indicating a movement of six places.3. Unit conversion is crucial in mathematics and science, as it enables us to switch between different units of measurement for precise calculations and comparisons.