Which of the following is a physical change? O Ice melts at 0°C.
Carbon combines with oxygen to form carbon dioxide.
A red substance is decomposed by heat to form
mercury and
oxygen.
Water is decomposed by electricity into hydrogen and oxygen.

What rule is used to determine how many covalent bonds an element can form? a. the number of covalent bonds is equal to six c the number of covalent bonds is equal to five minus the group number plus the group number b. the number of covalent bonds is equal to eight d. none of the above minus the group number select the best answer from the choices provided