Hello!
The number of 20-g ice cubes required to absorb 47 kJ from a glass of water upon melting is 7 icecubes
Why?
We are going to clear from the equation of the released heat, the mass of ice (m). The specific latent heat of fusion of ice is 336 kJ/kg:

So, 7 ice cubes are required to absorb that amount of heat from the glass of water.
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Answer:
Decomposition of aluminium oxide forms aluminium atoms and oxygen atoms.
Explanation:
<u>Decomposition reaction:</u>
When a single compound break down into two or more simpler products.
For example "AB" reactant undergoes decomposition to form "A" and "B" products.
The chemical reaction is as follows.

The given compound is aluminium oxide.
The decomposition reaction of aluminium oxide is a follows.

The balanced equation is as follows.

Therefore, Decomposition of aluminium oxide forms aluminium atoms and oxygen atoms.
I think Magnesium not sure because the relative atomic mass of magnesium is 24,31.
Well it depends how close the places are to the edges of tectonic plates. Also the damage caused from the Earthquakes has to do with how sturdy the buildings are and whether they were built to withhold such strong forces.