Leaded gasoline was banned in the US in 1996 up until now. This was implemented through the Clean Air Act of 1996.
No, leaded gasoline is not a heterogeneous mixture. It is actually a homogeneous mixture where the lead additive is uniformly distributed throughout the gasoline.
It depends what you mean by 'better'. Lead used to be added to gasoline to stop pre-ignition or detonation (which causes engine knock or 'pinking') but it was found to have very bad side effects environmentally and physiologically. most countries have banned the use of leaded gasolines, and modern gasoline have other ways of dealing with detonation. so i guess, unless you like bad air and bad health, unleaded is best.
In addition to the hydrocarbons present in normal gasoline, leaded gasoline contains tetra-ethyl lead or other lead alkyls for their anti-knock effect.
I don't think there is a way to visually tell the difference between leaded and unleaded fuel. However, leaded gasoline has become "extinct" and it is more likely that you have unleaded gasoline in the can.
It takes unleaded I think
In the US in 1950, the average price of a gallon of regular leaded gasoline was 27 cents.
The average price of a gallon of regular leaded gasoline in 1957 was $.31 cents.
The average price of regular leaded gasoline in 1961 was .31 cents per gallon.
Yes, it is unleaded. No gasoline sold for consumer vehicles in leaded.
Leaded gasoline.
Nowhere I know of. You can however buy a lead additive to add to unleaded fuel, at any auto parts store.