Changes of state occur when there is a change in:
a thermal energy
b. electromagnetic energy
c. chemical energy
d. electrical energy

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.