As a general rule if two bikes are in the same price range, the smaller of the two will be lighter. This because there is less material used in the smaller BMX due to it's much simpler construction.
But, when you head for the high end, a flatland or racing bike is going to be much lighter compared to a mountain bike.
A street bike is a type of BMX bike, so your question can't be answered.
There are MTBs with 20" and 24" wheels for smaller riders, which probably is the closest thing to what you're describing. These wouldn't be BMX bicycles though, since BMX bikes don't have gears and have a taller handlebar than a mountain bike.
There's no telling. The BMX is probably smaller, so it should be lighter. OTOH they're often amazingly chunkily built and can be surprisingly heavy.
A hyper is better
Yes
It's more a question of "different" than outright "better".If you want to use your bike to get around with, then a mountain bike with gears and bigger wheels is better. It will be faster, less fatiguing and offer greater rider comfort.But if you want to do BMX style riding, with jumps and tricks and that, then a BMX is a better choice.
Yes, if you can find the correct bottom bracket for the frame.
It will if you have bmx (or bmx style) cranks.
No such thing. Trials is a sub-sport of mountain biking, often called "mountain bike trials". It's a sport similar to motorcycle trials where one takes a light bike and hops around an obstacle course. You might have heard "BMX" and "trials" in the same sentence because a BMX bicycle can essentially make a good trials bike with minimal modifications.
A true race bike is probably lighter, and may have another brake set up than a "normal" BMX. also you might have different parts that make the bike itself heavier, like if you are comparing a street or dirt bike to a race bike the back rim on the street/dirt bike the axle is going to 14mm instead of 3/8 axle, but other than that theres really nothing but gearing
The Black Eye Renegade is a much better bike. It is lighter and more durable.
The main differences between a 20-inch and a 24-inch BMX bike are the size of the wheels and frame. A 20-inch BMX bike is smaller and lighter, making it easier to maneuver and perform tricks. A 24-inch BMX bike is larger and provides more stability and speed, making it better for racing and riding on rough terrain.