If in a typical thundercloud the bottom of the cloud is negatively charged, what is the sign of the excess charge on the ground

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Which are advantages of renewable resources? check all that apply. renewable energy supplies are completely reliable everywhere. some renewable resources will never be used up. little or no waste is produced by renewable resource plants. electricity can be generated in large quantities. many renewable energy facilities have lower operating costs.

Ihave a density of 1.61g/cm^3 and a mass of 28g. find the missing value