Im guessing it's (a) since the numbers go in chronological order and you read the periodic table left to right
The difference between the two is, well for one
Spectrum: The entire range that the "<em>waves" </em>could be such, as visible light, x-ray's and so on.
Waves: These are different because they aren't telling you or showing the entire spectrum just which they length that they are.
<em>It may confuse you but it makes sense to me (Sorry)</em>
The answer that best fits the blank is the term WAXING. The moon is waxing whenever it reaches to the period that its phases are transitioning from new to full. The answer is the first option. This is when it is more that half is illuminated. Hope this helps.
Gravity is the energy due to Earth pulling down on an object.
Answer:
The new voltage between the parallel plates of the capacitor is 18V, because for a constant electric field, doubling the space between the parallel capacitor plates, will also double the potential difference (voltage) between the plates.
Explanation:
ΔV = E*Δd
Where;
ΔV is the change in potential difference
Δd is the change in the distance between the parallel plates
E is the electric field potential.
Assuming a constant electric field; 
when the spacing between the capacitor plates is doubled, d₂ = 2d₁
v₂ = (v₁*d₂)/(d₁)
v₂ = (v₁*2d₁)/(d₁)
v₂ = 2v₁
v₂ = 2(9) = 18 V
Therefore, for a constant electric field, doubling the space between the parallel capacitor plates, will also double the potential difference (voltage).