Given a scientific passage and an answer, generate a question for the given answer.

Q: Passage: A single-replacement reaction is one in which an element replaces another element in a compound. An element is in either the solid, liquid, or gas state and is not an ion. The example below shows the reaction of solid magnesium metal with aqueous silver nitrate to form aqueous magnesium nitrate and silver metal. Answer: single-replacement reaction

A: In this type of reaction, an element replaces another element in a compound, and the element is in any state of matter but is not an ion?
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Q: Passage: Figure 2.43 Positions and velocities of a metal ball released from rest when air resistance is negligible. Velocity is seen to increase linearly with time while displacement increases with time squared. Acceleration is a constant and is equal to gravitational acceleration. Answer: acceleration

A: If a ball is released from rest when air resistance is negligible, velocity is seen to increase linearly, while what related property is a constant?
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Q: Passage: Electrons in the outermost energy level of an atom are called valence electrons. They determine many of the properties of an atom, including how reactive it is. Answer: valence electrons

A:
What do you call the electrons in the outermost energy level of an atom?
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