B. The unknown solution had the lower concentration.
Explanation:
Osmosis is a phenomenon in which the molecules of the solvent has a tendency to move through a membrane which is semipermeable from lower concentrated side to the higher concentration side, so that the concentrations on both sides of the membrane must be equal.
So the unknown solution may have lesser concentration than the isotonic solution so that molecules of that solution move from less concentrated side to the more concentrated side, so its level drops.
Ruler is the answer of this question
<span>The answer is paint. A dissoluble is a substance that breaks up a solute in the arrangement of an answer, and any dissoluble other than water is viewed as a non-fluid dissoluble. Some basic illustrations incorporate either, liquor, benzene, disulfide, carbon tetrachloride and CH3)2CO.</span><span />