What color does cobalt-oxide produce? a. blue-violet b. red c. yellow d. green?

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Which statement about hf is true? it is zero for any compound in its standard state. it is positive when the bonds of the product store more energy than those of the reactants. it is negative when a compound forms from elements in their standard states. it is zero for any element that is in the liquid state.

Which fossil fuel is mainly used for heating and cooking? a. electricity b. coal c. petroleum d. natural gas