Hello there! The correct answer is B) odor.
When you are wafting something, you're checking its smell in a careful way so you don't get harmed by potentially harmful chemicals. The odor of something is how it smells, or what smell it gives off, making this the correct choice. You can also eliminate A and D since the beginning of the question states that they are two clear liquids, so the color and texture won't differentiate one from the other. As well as this, it would not be C since it isn't smart to taste test chemicals in a lab, unless your teacher says it's okay.
I hope this helps and have a great day! :)
