Comparing the mass of the nucleus with the mass of the protons and the mass of the neutrons refers to what?
einstein’s theory of relativity
nuclear binding energy
the weak force
the strong force
mass defect

The best option in here is the mass defect. This is so because the mass defect is the difference between the particles of the nucleous weight and the nucleous itself. According to the equation E=mc^2, the mass defect is related the the binding theory. In order to calculate the mass defect of an atom you need to add up the masses of each proton and each of neutron that are present in the nucleus and then you substract the actual mass of the nucleus from the combined mass. That is why in mass defect you need the information given in your question. 

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf