Consider the symbol subscript b superscript a baseline upper x where x stands for the chemical symbol for an element. what information is given by a and b?

Explanation:

According to the periodic table chart, symbol of an element resides at the center of each box.

And, a number at the bottom of each symbol represents the atomic number of the respective element.

Whereas a number at the top of each symbol represents the atomic mass of the respective element.

For example, sodium is represented as in the periodic table. Hence, atomic number of sodium is 11 and its atomic mass is 23 g/mol.

Thus, we can conclude that subscript "b" shows atomic number and superscript "a" shows atomic mass.

i do not get it   at all

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.