Aparticular atom has 58 protons and 82 neutrons. what are the atomic number, mass number, and periodic table symbol of this isotope?

Atomic number: 58

Mass number: 140

Periodic table symbol: Ce

Explanation:

Remember that the number of protons is equal to the number of electrons and that is what determines what element is each atom, so for example the Atomic number will be determined by the number of protons or electrons, since in the example it has 58, that would be the atomic number, the mass number is the sum of the protons and the neutrons, in this cas it would be 28+82=140, and the periodic table symbol for the element with 58 as the atomic number is Ce and its called Cerium.

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.