Two pairs of dancers encounter each other on the dance floor. The couples switch partners with each woman now dancing with the other man. This situation is analogous to which kind of reaction?

Explanation:

This situation is analogous to a double replacement reaction. A double-replacement reaction occurs when parts of two ionic composites are exchanged, making two new composites. One characteristic of this kind of reaction is that there are two compounds as reactants and two different compounds as products. So, in this case we can relate with it because there are two new couples with the same members that formed the previous couples.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.

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.