1.
A red taillight, on the other hand, is just a white incandescent bulb covered by red plastic. Hence it is red by means of subtractive coloration; its spectrum is the long-wavelength third of a continuous rainbow.
3.
This is just conservation of energy. In order for the atom to gain 2.1 eV of energy, it must get that 2.1 eV from somewhere else. In this case, it gets it by absorbing a 2.1 eV quantum. This absorption process is what gives us spectral absorption lines.
4.
The main body of the Sun is indeed very hot, very dense, very opaque gas. (Remember, "opaque" doesn't mean "dark"; it just means that you can't see through it.) This gas acts as an incandescent object (a.k.a. blackbody), producing a continuous "rainbow" whose brightness peaks in the blue-green.
However, in order for this light to reach us, it must pass through the Sun's tenuous, cooler atmosphere. The atoms in this cooler region (called the photosphere) are able to absorb quanta whose energies are just right to boost the atoms to higher energy levels; hence such quanta do not make it to Earth. These missing energies -- or missing wavelengths, if you prefer -- are the "Fraunhofer" absorption lines we see.
In human terms, the photosphere isn't terribly cool: 5800 K But since the temperature of the Sun's core is about 15 million K, the photosphere is cooler, which is all that matters.
5.
A given transparent vapor produces the exact same pattern of emission lines (when heated) as absorption lines (when cool and viewed against the backdrop of a hot incandescent object).
Sodium atoms can jump from energy A to some higher energy B by absorbing quanta of the right energy (thus conserving energy); or else they can drop from B down to A by creating a quantum of the same energy. The key is that the quanta involved in emission and absorption spectra have the same energies -- so the corresponding light waves have the same wavelengths.
6.
This is a conservation of energy question. The smallest amount of energy the atom can lose is 1.1 eV, if it jumps from the 1.7 eV level down to the 0.6 eV level. Hence it must emit a 1.1 eV light quantum if it does this.
Note that I didn't include 0.0 eV as an allowed energy level, so the atom can't emit a 0.6 eV quantum by jumping from 0.6 eV down to 0.0 eV.
7.
Less than a decade after presenting his "planetary" model of the atom, Niels Bohr used it to explain the chemical properties of the elements in a way that is essentially correct even today. More precisely, he explained why the periodic table is periodic -- that is, why the chemical properties of the elements repeat as you list them in order of increasing atomic number.
The key is how many "valence electrons" (outermost electrons) the atom has, since these are the electrons that are most easily shared with or donated to or stolen from neighboring atoms -- and that, Bohr realized, is what chemistry is all about. He hypothesized that the electrons occupy concentric "shells" within an atom and that each shell can only fit but so many electrons: two in the innermost shell, eight in the second shell, etc. Furthermore, atoms "like" to have filled valence shells: this requires the lowest energy. So, for example, any element that has just one valence electron very much "wants" to give away that electron to some other atom: such an element (lithium, sodium, potassium, etc.) is highly reactive. Any element whose valence shell is one electron short of being full (fluorine, chlorine, bromine, etc.) is equally reactive, but for the opposite reason: it is dying to steal an electron from some neighboring atom -- such as sodium, hence NaCl (table salt, held together via an ionic bond). Other atoms, like oxygen and nitrogen and carbon, share electrons with their neighbors in order to feel as if their valence shells are full: covalent bonds. And atoms that already have full valence shells feel no desire to react with anything at all: the noble gases.
8.
Emission-line spectra depend primarily on the gas's chemical composition, thus providing us with an "atomic fingerprint" that can be used to identify just what kind of gas it is. (Ditto absorption lines.) Temperature is the main factor in blackbody radiation, not emission-line spectra.
9.
Emission lines are produced when electrons make "quantum leaps" from high energy levels to low energy levels. This means that they can't be produced unless some electrons are in high energy levels to start with. A hot gas is one whose atoms are moving energetically on average, and the resulting high-speed collisions can "boost" (or "excite") electrons to upper energy levels: some of the two colliding atoms' energy of motion is given to an electron within one of those atoms.
In a cool gas, on the other hand, most atoms move slowly and most collisions involve little energy. Upward quantum leaps, just like downward ones, are all-or-nothing affairs: either an electron gets all of the energy it needs to reach the upper energy level or else it stays put in the lower level. Close isn't good enough; no IOUs are accepted by Nature. Since low-energy collisions don't provide enough energy to excite electrons from the lowest level (or "ground state") to even the second-lowest level, the electrons stay in the ground state and no emission lines are produced.
10.
All of the choices are true but only the last three choices are odd. In Bohr's model of the atom, each electron, for some reason, can only move along circular orbits of certain sizes, with no other orbits allowed. This also means that an electron can't be any closer to the nucleus than the radius of the innermost allowed orbit, so it can't spiral into the nucleus -- even though Maxwell's equations imply that a circling (accelerating) electron should radiate away its energy as electromagnetic waves (light) and should spiral into the nucleus as a result.
Oddest of all, perhaps, is the idea that when an electron changes its energy, it does so instantaneously. This also follows from the restricted orbits idea: if the electron took even a nanosecond to move from an inner orbit, say, to an outer one, that would still be a nanosecond during which the electron was at an in-between, forbidden distance from the nucleus. How can a physical process happen instantaneously, in zero time? It's as if a car switched lanes in zero time, with absolutely no time spent gradually (or even rapidly) crossing the lane divider. There's no spacetime process involved, no motion through space over a finite time interval; there's just a start and a finish with no cause-and-effect actions happening in between to bring about the situation at the finish. This is the true weirdness of the "quantum leap."