An alpha particle is composed of

A. nothing
B. two protons and two neutrons
C. one proton and no neutrons
D. one neutron no protons

B. two protons and two neutrons

Explanation: Alpha rays are fast moving streams of positively charged particles which are shown to be helium nuclei represented by 4He2, having a mass number of 4, i.e., having 2 protons and 2 neutrons. Mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom. A helium atom has 2 protons and 2 neutrons in its atom.

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the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.