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Element

Explanation:

Other things on that list like alloy and compound can be broken down, but elements cannot

If it is made from solid silver then it is an element. If it is made from a silver alloy then it is a mixture. If it is a silver plated plate (i.e. a plate made from say, copper but with a thin layer of silver on top) then it is an element on top of an element.

Explanation:

I'm assuming you're talking about solid silver, so, i believe an element.

3 1/4 %

explanation:

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.