a cylindrical object has a diameter of 1.25 cm and a height of 6.48 cm. what is its volume? be sure to provide units and express your answer to the correct number of significant figures.

Achemical reaction (also known as a chemical change) produces substances that are chemically different from the starting materials. an example of a chemical reaction is the formation of water from hydrogen and oxygen gas. in a physical change, a substance changes its physical appearance but not its chemical identity. an example of physical change is the formation of liquid water from solid water, a familiar process called melting. physically, liquid water looks very different from solid water (ice) but the chemical identity, water, is the same for both. which of following changes that affect the composition of our atmosphere involve physical changes and which involve chemical reactions? oxygen gas changes to ozone during thunderstorms carbon dioxide is produced by the combustion of gasoline in an automobile engine. when coal, oil, and natural gas are decomposed in landsills they produce methane gas. freezing rain develops when a warm air mass overrides a cold air mass. fog forms from water vapor when the temperature drops below the dew point

Can someone me with questions 12 and 13 plz.

Which statement is true about this reaction? 14n+1h 15o it is a practical source of energy on earth. it occurs only outside the solar system. its product is heavier than each of its reactants. it shows the critical mass of an element.