Check my answer
which is not correct?
    1000 km = 1 m
 
    1000 ms = 1 s
 
    10 cm = 1 dm < - correct 100%
 
    1000 mg = 1 g
all of them look correct to me, what am i missing?

1000km = 1m

Explanation:

Because 1000m = 1km

The correct answer is A.  1000 km = 1 m

Explanation:

In science, there are different units to measure distance, time, temperature, among others. This often implies certain units are bigger/smaller than others, and therefore they need to be converted. In the case of distance, this is measured using centimeters, meters, kilometers, inches, etc, although the two more common units are meters and kilometers. In this case, kilometers cover a bigger distance than meters; indeed, there are 1000 meters in one kilometer which means 1000 m or m = 1 km and therefore it is not correct that 1000km = 1 meter as 1000 km are equivalent to 1,000,000 m considering 1000 km x 1000 m (number of meters in each kilometer) = 1,000,000.