Shielding electrons are the electrons in the energy levels between the nucleus and the valence electrons. They are called "shielding" electrons because they "shield" the valence electrons from the force of attraction exerted by the positive charge in the nucleus. Hope this helps!!
A raised weight.
Water that is behind a dam.
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I believe the answer is A
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If the reaction could be made to go faster B. The hill would be shorter.
The "hill" is called Activation Energy. It is the energy of the activated intermediate compound needed to complete the reaction. Catalysts are substances that don't intervene in the reaction which speed up the rate of a given reaction by lowering the Activation Energy giving alternate reaction pathways with lower-energy intermediates. If the reaction could be made to go faster with the use of a catalyst, then the Activation Energy would be lower and the "hill" would be shorter.
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