Answer:
Sodium Aluminate
Formula:-

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Melting points and boiling points of some ionic compounds

2, 8,6 because it has to be in a configuration of 2,8,8
MgH2 + 2 H2O → Mg(OH)2 + 2 H2
W=F*d
W= 500 J
F = 250 N
500 J = 250 N * d
d= 500J/250 N = 2 J/N = 2(N*m)/N = 2 m
Answer is 2 m.