Which is a question which science cannot answer? how does the moon affect tides on earth? how long does it take for the earth to rotate on its axis? when will the next earthquake happen? why do volcanoes erupt?

Till now we are able to find

a)  How does the moon affect tides on earth? : the answer is moon gravitational field

b) How long does it take for the earth to rotate on its axis? : we know the answer is 24 hours (a day)

c) Why do volcanoes erupt? : due to divergence / convergence of tectonic plates

However we still cannot predict "When will the next earthquake happen?" based on science

the answer is b. dilution

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.