The image shows four elements in the periodic table: Sodium (Na), Magnesium (Mg), Potassium (K), and Rubidium (Rb). Which among the following shows the elements correctly ordered by increasing atomic radii?

• Mg < K < Na < Rb

• Mg < Na < Rb < K

• Mg < Na < K < Rb

• Rb < Na < K < Mg

The chemical equation for the combustion of methane is: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat. Which statement correctly describes this combustion reaction?

• The energy absorbed by breaking chemical bonds is less than the energy released by bond formation.

• The energy released by breaking chemical bonds is less than the energy absorbed by bond formation.

• The energy absorbed by breaking chemical bonds is greater than the energy released by bond formation.

• The energy released by breaking chemical bonds is greater than the energy absorbed by bond formation.

The following equation represents the acid-base reaction between hydrochloric acid and sodium hydroxide solution: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l) + Heat energy. Which statement correctly explains the energy change during this reaction?

• The energy required to break the bonds of the reactants is less than the energy required to form the bonds in the products.

• The energy required to form the bonds of the reactants is less than the energy required to break the bonds in the products.

• The energy required to break the bonds of the reactants is greater than the energy required to form the bonds in the products.

• The energy required to form the bonds of the reactants is greater than the energy required to break the bonds in the products.

The chemical equation for the decomposition of silver chloride is: 2AgCl(s) + energy → 2Ag(s) + Cl2(g). Which statement is correct based on this equation?

• The reaction is exothermic because energy was needed to break the chemical bonds in AgCl.

• The reaction is endothermic because energy was needed to break the chemical bonds in AgCl.

• The reaction is exothermic because energy was needed to form the bonds in Ag and Cl_2.

• The reaction is endothermic because energy was needed to form the bonds in Ag and Cl_2.

Why is it necessary to keep fresh milk refrigerated instead of storing it on a kitchen counter?

• The chemical reactions that cause milk to spoil progress at a slower rate at lower temperatures.

• Milk tastes better when it is cold than when it is warm.

• Milk will evaporate if it is not kept cold.

• Milk is a mixture, so the compounds that it is made of will separate at higher temperatures.

Which statement best describes the relationship between temperature and the rate of a chemical change?

• Increasing the temperature increases the energy of reactant particles, which causes more frequent collisions and a faster reaction rate.

• Increasing the temperature causes the reactant mixture to expand, decreasing the collision frequency and slowing the reaction rate.

• Increasing the temperature causes molecules to break apart and the reaction rate to slow to zero.

• Increasing the temperature does not affect the reaction rate because the particles move faster, but they are farther apart.

Copper and gold have similar reactive properties. On the periodic table of the elements, these elements are most likely to

• be in the same group.

• be in the same period.

• have nearly the same mass.

• have the same number of protons.

Electrical breakdown is a process by which an insulator begins to act like a conductor at high voltages. Which observation would BEST indicate that electrical breakdown has occurred in a material touching a conducting wire?

• The material starts to darken in color.

• The material starts to attract a magnet.

• The material begins to emit a smoky odor.

• The material begins to decrease in temperature.

The circuit below is used to test four different solutions.

• the most concentrated electrolytic solution and the best insulator

• the least concentrated electrolytic solution and the best insulator

• the most concentrated electrolytic solution and the best conductor

• the least concentrated electrolytic solution and the best conductor

Why are metals good conductors of thermal energy?

• The randomly arranged atoms in metals increase the ability to transmit heat.

• The atoms in metals can easily convert chemical energy into kinetic energy.

• The freely moving electrons in atoms transfer kinetic energy throughout the metal.

• The electronegativity difference between atoms in metals allows heat to flow easily.