This would be more of a chemistry question. Remember magnesium has a charge of 2+, and would need to hand off its two extra electrons. Fluorine can only take one electron at a time, so there needs to be two fluorines to take one magnesium's 2 electrons.
With lithium, it has a +1 charge, so it has one extra electron, which it can hand off to just 1 fluorine atom.
Another way of looking at this is:

+ 2

= MgF2 (the charges must balance out to zero)

+

= LiF (the charges balance out to zero)
The atomic number is the same as the proton number so the answer would be D) 10
Answer:
gexp = 3.65 m/s²
Explanation:
The value of acceleration due to gravity changes with the altitude. The following formula gives the value of acceleration due to gravity at some altitude from the sea level:
gexp = g(1 - 2h/Re)
where,
gexp = expected value of g at altitude = ?
g = acceleration due to gravity at sea level = 9.8 m/s²
h = altitude = 2000 km = 2 x 10⁶ m
Re = Radius of Earth = 6.37 x 10⁶ m
Therefore,
gexp = (9.8 m/s²)(1 - 2*2 x 10⁶ m/6.37 x 10⁶ m)
<u>gexp = 3.65 m/s²</u>
<span>Energy is neither lost nor gained as it transforms from chemical, to heat, to mechanical energy.</span>