Chemical Structure

I suppose you can try to dissolve each crystal in a solvent (water) and see which one conducts electricity. The salt will conduct electricity whereas the sugar won't. Also, adding salt to water will change its boiling and freezing temperatures. For instance, water will freeze at lower temperatures than zero degrees celsius when you dissolve salt in it. This means there is less chance of ice forming when salt is added than when sugar is added. This effect doesn't occur when you dissolve sugar. In addition, salt crystals are more regular and look more square, while sugar crystals are more irregular in shape.  Look at crystals of both with a magnifying glass and you'll see the difference.

Makes sense?

Bio_man 8)

Yepp, Can you please delete this thread now?

Please do not delete your question. That demeans the whole purpose of this website.