Model in which electrons are found in fixed levels around the nucleus and require energy to move from level to level:
a. bohr model
c. quantum mechanical model
b. rutherford model
d. free-electron model

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explanation:

warm front forms when a moist, warm air mass slides up and over a cold air mass. as the warm air mass rises, it condenses into a broad area of clouds. a warm front brings gentle rain or light snow, followed by warmer, milder weather.

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