Answer:
Pyrophoricity is a property of metals and oxides of lower oxidation states, including radioactive ones, in which they spontaneously ignite during or after stabilization.
A. Cs - 55 electrons, 55 protons, 77 neutrons
B. Co - 27 electrons, 22 protons, 32 neutrons
C. Tm - 69 electrons, 69 protons, 94 neutrons
D. Zn - 30 electrons, 30 protons, 40 neutrons
For any neutral atom, protons = electrons = atomic number. Neutrons = atomic mass - atomic number.
Answer:
1.2km=1,200,000! hope this helps