Acollection of coins contains 15 pennies, 12 dimes, and 7 quarters. what is the percentage of pennies in the collection?
express your answer to two significant figures and include the appropriate units.

Calculate the percent composition by mass of each element in al(oh)3. use at least three significant figures.

Covalent compounds: mastery test select the correct answer what is formed when atoms join together with a covalent bond? a. an ion b. a molecule c. a neutral atom d. a noble gas

Use the periodic table to answer the following questions. what is the predicted order of first ionization energies from highest to lowest for beryllium, calcium, magnesium, and strontium? o be > ca > mg > sr o be > mg > ca > sr o ca > sr> be > mg o sr > ca > mg > be done