$\text{Weight of 1 dumbbell}=800\text{g}$$\Rightarrow \text{Weight of 4 dumbbells}=800\text{g}\times 4$
                                             $=3200\text{g}$

Since the options are in kilograms, we need to convert 3200 g to kg.

When we convert a smaller unit (g) to a larger unit (kg), we divide the given measure by the conversion factor.
         $1\text{kg}=1000\text{g}$
$\Rightarrow 3200\text{g}=\frac{3200}{1000}\text{kg}$
                 $=3.2\text{kg}$
Thus, the weight of 4 dumbbells is 3.2 kg.