All elements in a period have the same energy level due to which of the following reasons?

a. the same atomic number

b. the same number of neutrons

c. the same number of electrons

d. the same number of electron shells

An oil refinery plans to separate a mixture that contains propane and octane, shown below, by vaporizing the mixture and then collecting the substances as they cool and condense. 1. Will propane or octane condense at a lower temperature?

Which change will always result in an increase in the avitational force between two objects? increasing the masses of the objects and increasing the distance between the objects decreasing the masses of the objects and decreasing the distance

What is a tough, rigid, outer covering that protects some cells and gives them shape?

One liter equals the volume of a cube ten centimeters on a side

When a solid melts a. the temperature of the substance increases. b. the temperature of the substance decreases. c. heat energy leaves the substance. d. heat energy enters the substance.?

What is an isotope? Give an example of an element with isotopes.

Consider the reaction between liquid water and aqueous magnesium nitride to form solid magnesium oxide and ammonia gas. If magnesium nitride is present in excess, how many moles of water are needed to form 9.17*1023 ammonia molecules?

The properties of elements are arranged by ... A. mass numbers B. atomic masses C. atomic radii D. atomic numbers

When a tire is inflated with air is it a chemical or physical change?

Which isotope is used to date ancient artifacts such as fossils? carbon-12 carbon-14 uranium-238 oxygen-16