Your own definition for plate tectonics

The two sub-layers of the earth's crust (lithosphere) that move, float, and sometimes fracture and whose interaction causes continentaldrift, earthquakes, volcanoes, mountains, and oceanic trenches

D=m/v =57.9/3 = 19.3 g/cm^3

B.1 - hydrogren-1 can only mean there is 1 neutron. it's obvious there is 1 proton or else it wouldn't be hydrogen, so they wouldn't put a number after it unless they were indicating the number of neutrons