When the electron from the n=4 excited state drops to the ground state, does it absorb energy or emit energy?

Different isotopes indicate that an element will have different numbers of

The comparison of the number of atoms in a copper coin the size of a penny with the number of people on earth is made to illustrate which of the following? a. that atoms are indivisible b. that atoms are very small c. that atoms are very large d. that in a copper penny, there is one atom for every person on earth

What type of chemical bond is formed between two atoms of bromine 1. metallic 2. hydrogen 3. ionic 4. covalent