State Identification (States of significance)

Question

Here is a short identification puzzle inspired by a road trip across the U.S.

There are four sets of clues, each identifying a state.
Please identify each state and what they have in common/why they specifically are significant.
A clue or set of clues may have multiple possible answers, but only one combination forms a complete answer.

a)

• Not one of the original states
• is on its right
• could fit within it
• The last letter is the same as the first letter
• 
• Imports false charity into the Keystone State

b)

• Near
• Nearly
• Associated with cars and also pollution
• Quite low density

c)

• Potatoes, say
• Imports crude petroleum into the Mount Rushmore State
• Has a recognizable shape
• Contains part of the mind (Freudian)

d)

• 
• Has more freedom than (c)
• Forms part of Lake Superior
• 
• Also contains a part of the mind

Hint:

Little or no knowledge is required to solve this puzzle. There are a few viable break-in points (in my opinion); solving any will quickly lead you to the answer.

Answer 1

These four states are...

the four states of matter! From OP: matter is a synonym for "significance", as per the title

The first state is...

Plasma

Explanation:

Plasma isn't one of the "original" states of matter (solid, liquid, and gas). Massachusetts is on its right (plasMA), and Louisiana could fit within it (pLAsma). The last letter (in "plasma") is the same as the first (in the alphabet). Hidden from Arizona's flag is a star, and stars are made of plasma. "Imports false charity into the Keystone State" is almost a cryptic clue, where "charity" = "alms": P(LASM)*A.

The second state is...

Gas

Explanation:

Montana's abbreviation is "MT", and fuel gauges have "empty" on them from OP: gas is mostly "empty" space. "GAs" is nearly Georgia (GA). Gas is used to fuel cars, pollution is commonly gaseous, and gas is quite low density.

The third state is...

Solid

Explanation:

Potatoes are an example of a solid. "Imports crude petroleum into the Mount Rushmore State" is another almost-cryptic-clue, where "petroleum" = "oil": S(OLI)*D. Solids can hold their shape (and thus have recognizable shapes) and contain part of the mind, according to Freud: solID.

The fourth state is...

Liquid

Explanation:

Lakes are generally liquid, and can change their shape more easily than solids. You can have liquid assets and river banks, but deserts and brick houses are usually dry? From OP: "Stocks and cash/cash accounts are considered liquid assets; land and buildings are not." Liquids also contain part of the mind, according to Freud: liquID.