Which of the following molecules is unable to form hydrogen bonds with water?A.CH3BrB.CH5NC.C2H6O2D.HF

To answer this question, we need to understand what hydrogen bonding is. Hydrogen bonding is a special type of dipole-dipole attraction between molecules, where a hydrogen atom bonded to a strongly electronegative atom such as nitrogen, oxygen or fluorine experiences attraction to some other nearby highly electronegative atom.

Let's analyze each option:

A. CH3Br - This molecule has a bromine atom, which is not highly electronegative enough to form hydrogen bonds with water.

B. CH5N - This molecule doesn't exist. The maximum number of bonds that nitrogen can form is 3, so it can't bond with 5 hydrogen atoms.

C. C2H6O2 - This molecule, also known as ethylene glycol, has two hydroxyl (-OH) groups, which can form hydrogen bonds with water.

D. HF - This molecule has a hydrogen atom bonded to a fluorine atom, which is highly electronegative and can form hydrogen bonds with water.

So, the molecule that is unable to form hydrogen bonds with water is CH3Br (option A).