<span>B. 51 50
Z and Z
25 25
It is because only this element have equal number of Protons (Bottom number) and are different in atomic masses (upper number)
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It would of been nice if you were to post your question so others could actually answer it.
Answer:
Volcanologists use many different kinds of tools including instruments that detect and record earthquakes (seismometers and seimographs), instruments that measure ground deformation (EDM, Leveling, GPS, tilt), instruments that detect and measure volcanic gases (COSPEC), instruments that determine how much lava is moving underground (VLF, EM-31), video and still cameras, infrared cameras, satellite imagers, webcams, etc!
Explanation:
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