The diagram shows four different locations in an atom.
a shaded circle is shown, labeled nucleus. two small points labeled two and three are shown inside this shaded circle. a lighter shaded concentric circle is shown with a radius more than double of the radius of the inner circle. a point labeled one is shown inside a section of this circle which does not overlap with the inner circle. a flower petal like shaded region is shown above and below these circles. a point labeled four is shown inside the lower petal.
which locations are likely to have subatomic particles with the greatest mass?
1 and 2
2 and 3
1 and 4
3 and 4

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.