A C and D are all correct, Helium and Hydrogen only have a 1s orbital, and helium has 2 protons, while hydrogen has 1, and finally Hydrogen has no neutrons while helium has 2. Helium does not however have 8 valence electrons as the 1s orbital can only hold 2, meaning B is the “correct” (false) answer.
By definition, motion is the change of position over time. The obvious answer would be
<span>
A change in position over a certain amount of time.
If we investigate the choices, the first one talks about acceleration. That is delta velocity over delta time. The third choice is simply distance. And the fourth one is just a point in space used as a reference.
I hope I was able to explain it clearly :)</span>
pH = 4.82
[H⁺] = 1.5 × 10⁻⁵ mol·L⁻¹.
pH = -log[H⁺] = -log(1.5 × 10⁻⁵) = 4.82