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> .. What, materially, is that property ..

Synapses firing ..

> .. what physical laws explain it ..

Physics ..

> .. and by what mechanism does it emerge from mere electrical impulses?

Through the senses and acting on the environment through muscles triggered by synapses firing.

Heard of the China brain thought experiment? https://en.m.wikipedia.org/wiki/China_brain

Would such a brain be conscious? Why or why not?

> Would such a brain be conscious? Why or why not?

If the brain was stimulated by inputs from the surrounding environment then YES!