is the chemical formula for benzene and is the most stable out of the answer choices because it is the only listed molecule that is aromatic.

In most cases, negatively charged compounds are ranked as more basic, while positively charged compounds are deemed as more acidic. If two compounds have the same charge, we begin to look at the sze of the atom, then stabilization provided by resonance, then dipole induction.

The compound with the lowest  is always the most acidic. In this case, the electronegativity difference between hydrogen and chlorine is very large, and so the proton can dissociate very easily. This is why refer to  is a strong acid. Note that  is the only strong acid that is given as an answer choice.

Because of the visible attachments on the nitrogen, we might initially think that  assumes a trigonal planar shape, and is therefore planar. However, because there is no formal charge on , we know that there must be a lone pair present on the nitrogen atom. The lone pair can be thought of as another attachment, and so the  assumes a tetrahedral shape instead. Tetrahedrals are non-planar.

This nitrogen can be thought of as having 4 attachments: one carbon, two hydrogens, and one lone pair. The nitrogen assumes a tetrahedral shape and is sp³ hybridized.

When discussing solubility, remember the phrase, "like dissolves like."

Hexane, being made of solely carbons and hydrogens, is extremely nonpolar. Thus, our correct answer must also be nonpolar, as like dissolves like. Although carbon tetrachloride is made up of four polar bonds, the net charge on the molecule is zero, as the polar bonds all pull in equal and opposite directions. All other answer choices are polar, and thus insoluble in hexane.

We can answer this question simply by glancing at the periodic table. As a general trend, elements are more electronegative the more we move up to the "north-east" corner (stopping at fluorine), with fluorine being the most electronegative atom. Of the provided answer choices, oxygen is the most electronegative.

We can solve this problem using process of elimination. Right away, we can eliminate answer choice 2, as it is the only molecule that is not conjugated (increased conjugation leads to increased stability). Next, we can rule out answer choice 3, as it is less conjugated than the other two remaining options. Finally, we can arrive at answer choice 4 as our correct answer, because not only is this molecule the most conjugated, it is also aromatic. Aromatic molecules are highly stable. Recall that aromatic compounds follow the Huckel rule of pi electrons: 4n +2.

Carbocations are most stable when they are most substituted. The carbon at position 2 is the most substituted carbon on the pictured molecule and would produce a tertiary carbocation. This is due to the fact that R-groups are electron-donating groups, and a carbocation is electron-deficient, thus the more R-groups adjacent to the carbocation, the more stable it will be.

We can eliminate  and  right away because they are not a strong acids, while the other answer choices are (memorizing strong acids and bases is recommended in most organic chemistry courses).

From here, we can methodically find the correct answer by comparing each answer choice's conjugate base. It is easier to compare base strength than acid strength and the stronger an acid's conjugate base, the weaker the acid (vice versa).

 is the largest conjugate base of the two choices. In this case, the large size of the bromine ion allows the negative charge to be dispersed more through the atom, providing stability. This stability makes it the weakest conjugate base and the strongest acid.