Answer:
There are 10.0 moles of beryllium oxide in a 250 grams sample of the compound.
Explanation:
We can calculate the number of moles (η) of BeO as follows:

Where:
m: is the mass = 250 g
M: is the molar mass = 25.0116 g/mol
Hence, the number of moles is:

Therefore, there are 10.0 moles of beryllium oxide in a 250 grams sample of the compound.
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Answer:
oxygen ion O2-
Explanation:
because it has 8 protons and gave gained 2 electron so O2-.
Tungsten (W) has an atomic number 74
The nearest noble gas to tungsten in the periodic table is Xe which has atomic number of 54.
Therefore, the configuration of W using the noble gas Xe will be as follows:
<span>[Xe] 4f14 5d4 6s2</span>