Which of the following is a physical change? O Ice melts at 0°C.
Carbon combines with oxygen to form carbon dioxide.
A red substance is decomposed by heat to form
mercury and
oxygen.
Water is decomposed by electricity into hydrogen and oxygen.

h let me think

it should be all of them because it asks if you included all of those in your answer

explanation:

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.