How do chemists know that an oxygen molecule have unpaired electrons?

They know that it has two unpaired electrons because of the position of the valence electrons and their structure. 2 of the final positions both have only 1 electron because they always have to be filled first with at least 1.

It conforms what ever surface its in.

Firstly, the water in the dams hold gravitational potential energy as they are above ground level. the gravitational potential energy is then transferred to kinetic energy as it falls, spinning the turbinethe turbine then spins the generator, which is a large magnet surrounded by metal coils. by doing this, the generator generates electricity. in this action, the energy transfer taken place is kinetic to electric energy