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How many protons are present in a neutral atom of bromine?
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2. Atoms & Elements
The Atom
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Which of the following best describes the composition of cathode rays?
A
Alpha particles
B
Streams of electrons
C
Neutrons
D
Streams of protons
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Recall the historical experiments related to cathode rays, such as J.J. Thomson's cathode ray tube experiment.
Understand that cathode rays are streams of particles emitted from the cathode (negative electrode) in a vacuum tube when a high voltage is applied.
Recognize that these particles were found to have a negative charge and a very small mass compared to atoms, which led to the discovery of the electron.
Eliminate options that do not fit this description: alpha particles (positively charged helium nuclei), neutrons (neutral particles), and protons (positively charged particles).
Conclude that cathode rays are best described as streams of electrons, which are negatively charged subatomic particles.
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