Because Na⁺ ion lacks an electron and O²⁻ has two extra electrons extra, to balance the charge, we need 2 Na⁺ ions.
All ions, atoms and molecules want to get to the minimum energy state, and that state is when the ion, atom, or molecule is neutral, that's why all of them want to balance their charges.
Efficiency is calculated through dividing the actual mechanical advantage by the hypothetical mechanical advantage:
- the actual mechanical advantage is 9J because that's how much work the light bulb doing
- the hypo. mechanical advantage is 100J. Ideally, in a perfect world, the light bulb can convert 100J input into 100J output, but do to resistance and other factors it is not possible.

change the decimal to a percentage:

the light bulb had 9% efficiency
Answer:
satellite B
Explanation:
A .F= G (mM)/r²
B .F= G (2mM)/r² = 2G (Mm)r²
C .F= G (3mM)/(2r)² = ¾G (mM)/r²
D .F= G (4mM)/(2r)² = G (mM)/r²
Answer: It would destroy the Earth's surface.
I remember reading this questions in What If? by Randall Munroe. Great book, I suggest you check it out. Anyway, the answer. The Earth is revolving as well as spinning on its axis at the same time. This basically means that thee atmosphere is also spinning at the same speed. But due to the frame of reference, we don't notice anything. If the Earth suddenly stops spinning, then the atmosphere, going according to the first law of motion will still be spinning at the same speed. This would produce supersonic winds at such a scale that it will be compared to an atomic explosion. Anything not in a nuclear bunker will probably be ripped apart by the force of the wind.