The__ model assigns to fixed orbits of defined energy. To move between orbits, electrons must emit or absorb radiation

The Bohr model assigns to fixed orbits of defined energy. To move between orbits, electrons must emit or absorb electromagnetic radiation

Explanation:

In the Bohr model of the atom, the atom itself looks like a solar system.

In fact, at the center of the atom we have the nucleus, which contains protons and neutrons.

Around the nucleus, at a much higher distance, we have the electrons, negatively charged. The electrons move around the nucleus in fixed orbits, like the planets around the Sun.

According to Bohr's model, the electrons  cannot live in the space between two orbits, but they must stay in one of these orbits. Each of these orbits is associated to a certain energy level: therefore, this means that the energies of the electrons in an atom are quantized, so they cannot take all possible values, but only some precise values.

Moreover, according to the law of conservation of energy:

- When an electron jumps from a lower energy level to a higher energy level, it must absorbs energy, and this energy is absorbed in the form of electromagnetic radiation (a photon) whose energy is equal to the difference in energy between the two levels

- SImilarly, when an electron jumps from a higher energy level to a lower energy level, it releases energy, in the  form of electromagnetic radiation (a photon) whose energy is equal to the difference in energy between the two levels.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.