What will be the number of atoms in 0.750 gram of fe

8.085x10²¹ atoms

Explanation:

Atomic mass of Fe = 55.845 g/mol

it means ,

1 mole Fe = 55.845 g

1 mole = 6.02x10²³  atoms

so,

55.845g Fe has = 6.02x10²³ atoms

∴0.750 g  Fe has = {(6.02x10²³ x 0.750)/55.84} atoms

                             =8.085x10²¹ atoms

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.