Which of the following explains why the substances cannot dissolve in water?
sugar, because it is an ionic substance
oil, because it is a nonpolar covalent substance
sugar, because it is a nonpolar covalent substance
oil, because it is an ionic substance

Oil, because it is a nonpolar covalent substance  

Explanation:

Water molecules are so strongly attracted to each other by hydrogen bonding that nonpolar molecules cannot get between them .

A and C are wrong. Sugar is a polar covalent substance.

The substance oil cannot dissolve in water because it is a non polar covalent substance.

It is known that water is a polar solvent with weak vanderwaal's bonding.

So the elements which are soluble in water should also be polar in nature.

As a solute can dissolve in a solvent only and only if they have same polarity.

The solute having different polarity with the solvent will not dissolve in the solvent leading to floating of the solute or suspension of the solute over the surface of the solvent.

The best example is oil floating in water as oil is non-polar and water is polar in nature.

So the difference in polarity resists the substance i.e., oil to dissolve in water and the oil floats on the surface of water.

Thus the substance which cannot dissolve in water among the given options were oil due to its non-polar nature.

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