On a test, helena is defining energy. which must she include in order to get her answer marked correct?

making objects more compact

the ability to do work

carrying through matter and space

the bonds of atoms

The phrase, which Helena must include in order to get her answer marked correct is: THE ABILITY TO DO WORK.

Generally, energy is defined as the ability to do work. It is the fundamental force that is required to move things around, to accomplish tasks and to do several other things. Energy exist in different forms and it can be converted from one form to another form but it can not be created or destroyed. Humans derived energy from the food they eat. The energy in food is called chemical energy; this energy is converted to other types of energy as the needs arise. The SI unit of energy is Joule.

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

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.