How is the density of a substance calculated

One statements is an example of a scientific observation. another statement is an example of a scientific explanation. identify the correct statement for each category to illustrate how scientific explanations are inferred from scientific observations.

Which of the following statements is true? 1. the mantle of the earth is made of solid nickel and iron. 2. the crust of the earth is made of solid nickel and iron. 3. the inner core is made of solid nickel and iron.

Biomass can be used to generate electricity. biomass relies heavily on agricultural crops. plants release carbon dioxide and water in combustion. plants use photosynthesis to originally generate the energy that is needed. the chemical energy of these plants all started with what energy source?