#### Answer

a. 0.5 kg

#### Work Step by Step

A weight of 0.5 g is less than the weight of 1 tsp of water. Clearly a box of cereal is heavier than this weight.
A weight of 0.5 t is hundreds of kilograms which is clearly too heavy for a box of cereal.
A weight of 0.5 kg is the weight of half a liter of water. This seems like a good estimate for the weight of a box of cereal.
The best estimate for the weight of a box of cereal is 0.5 kg