Once heat from the sun penetrates the earth's atmosphere, the heat is circulated as warm air rises and cold air sinks. what is this process called?

a. radiation b. conduction c. reflection d. convection

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When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?