The petrol additive tetraethyl-lead (IV), Pb(C2H3)4, is now banned in many countries. When it is completely burned in air,
lead (II) oxide, CO, and H2O are formed. How many moles of
oxygen are required to burn one mole of Pb(C2H5)?

When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon. the wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. these emitted photons form the element's spectrum.

Energy is a force, and just like any other, it has the effect of gravity. a bond holds things together, so the greater the force, the stronger the bond. this means that more energy equals stronger bonds. the greater gravitational force will strengthen the bonds, so larger atoms with more gravitational force will greater stronger bonds. i believe this is the correct answer, sorry for the incorrect one.  hope this ! answer: a