School and Work

Which member of the following pairs of compounds would you expect to have the higher lattice energy? Explain why?

1)Calcium chloride or magnesium floride

2)lead(II) bromide or lead(iv) bromide

3) sodium phosphide or sodium phosphate

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QUESTION:
- CMB hot spots have matter density that is about 10^-5 higher than the background average.
Let us consider the evolution of such a hot spot with the opposite assumption as above.
Assume the matter density in the hot spot is sufficient to resist the cosmological expansion and therefore remains constant, while the rest of the universe expands as
a = t^2/3
Compared to today's mean matter density in the universe (30% of the critical density),
how much higher is the matter density in these hot spots today?

it has something to with the density of background = t^-2, and i'm supposed to calculate the ratio based on the times

PLEAAAASEEE HELPPPPP

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