GPE is the gravitational Potential Energy which is given by mgh.
mg is the gravitational force(a force) and h is the height of the object(or distance of the object from earth's surface)
SO GPE = mg (force) x h (distance)
Answer : The correct option is, (D)
Explanation :
Option A reaction : 
It is a combustion reaction. A reaction in which a hydrocarbon react with the oxygen to give product as carbon dioxide and water.
Option B reaction : 
It is a combination reaction. A reaction in which the two or more reactants react to give a product.
Option C reaction : 
It is a decomposition reaction. A reaction in which a reactant decomposes to form two or more products.
Option D reaction : 
It is a single displacement reaction. It is a reaction in which the more reactive element displace the less reactive element. In this reaction, most reactive element chlorine displaces the less reactive element bromine.
Hence, the correct option is, (D)
Mole ratio:
MgCl₂ + 2 KOH = Mg(OH)₂ + 2 KCl
2 moles KOH ---------------- 1 mole Mg(OH)₂
moles KOH ------------------- 4 moles Mg(OH₂)
moles KOH = 4 x 2 / 1
= 8 moles of KOH
molar mass KOH = 56 g/mol
mass of KOH = n x mm
mass of KOH = 8 x 56
= 448 g of KOH
hope this helps!
ok so this was really confusing, but i think i know the answer. D. ...hairy and ancient hermit crabs and swift, darting minnows and sometimes a
crumbling sand dollar.