I think the answer is d. In the magnetotail. I hope this helps! :)
Pour the entire components into water.
First the iron filings can be separated using a magnet as iron is a magnetic element.
By pouring the mixture into water, it allows the salt to dissolve in the water, while the sand will not.
Next we can run this solution through a filtration device to separate the sand from the water.
Now all that's left is to let the water evaporate so that the salt will be exposed that dissolved into the water.
