The equivalence point during titration of an acid with a base may not occur at a pH of 7.0 because 1. if a strong acid or base is used, it is completely ionized and therefore not neutral. 2. the indicator may be one that changes color at some other pH. 3. The statement is false; the pH must be 7.0 at the equivalence point. 4. hydrolysis of the salt produced may make the solution acidic or basic. 5. A solution containing a weak acid or a weak base could never be neutral

a electronegativity decreases beacuse the size of nucleus is bigger.

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.