Answer:
Scientists believe that comets are the debris left from the solar nebula which condensed to form the Sun and planets in our solar system. Most comets are thought to originate in a huge cloud called the Oort Cloud. ... Comets follow a regular orbit around the Sun.
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Explanation:
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Answer:
the reactivity of alkaline earth metals increases from top to the bottom of the group, that's because the atoms get bigger from the top to the bottom so the valence electrons are farther from the nucleus.
B. A pure substance made up of one type of atom
Answer:
Ionic bond is the electrostatic attraction among the positive and negative ions.
Explanation:
It forms when the valance electrons (electrons in the outer shell) of one atom are transferred to another atom.
