Answer:
Electron
Explanation:
See attached figure (it was missing in the question).
An atom consists of three types of particle:
- Proton: it is positively charged (charge [tex]+e = +1.6\cdot 10^{-19} C[/tex]) and it is located in the nucleus. Its mass is approximately [tex]1.67\cdot 10^{-27} kg[/tex]
- Neutron: it has no electric charge, and it is also located in the nucleus. Its mass is just slighly larger than that of the proton (but it is also approximated to [tex]1.67\cdot 10^{-27} kg[/tex])
- Electron: it is negatively charged (charge [tex]-e = -1.6\cdot 10^{-19} C[/tex]) and it orbits around the nucleus. Its mass is much smaller than that of the proton ([tex]m_e = 9.11 \cdot 10^{-31} kg[/tex])
From the figure, we see that the only particle orbiting around the nucleus is particle A: therefore, A must be an electron.
