C) They each form similar compounds when combined with oxygen.
Explanation:
The given elements have a common characteristics as they each form similar compounds when combined with oxygen.
Beryllium, magnesium and calcium all are located in the alkaline earth group.
Elements in the same group have the same chemical properties.
- Density and melting point are physical properties of matter which varies down a group on the periodic table.
- Their reaction with oxygen denotes a statement of their chemical properties.
- Chemical properties of matter is a function of their valency.
- Group two elements have a valency of two. They have two electrons in their outermost shell.
- Therefore, they all form ionic bonds when they react with oxygen.
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Answer:

Explanation:
Chemical Equations are representations of chemical reactions in terms of the symbols and formulae of the elements and compounds involved. A chemical equation usually have the reactant at the left hand side while the product is on the right hand side.
A chemical Equation is of little or no value if is not in balanced equation. When an equation is balanced , the total number of atoms of any element on the left-hand side of it must be equal to the total number of atoms of that element on the right hand side.
in the given question; we are given a word problem of chemical symbol to compute and also to balance the chemical equation.
From below; the chemical equation can be written as:

From the above equation we will notice that it is not truly balanced ; so th balanced equation can be written as:

There is 6.02*10^23 molecule per mole. And there is 2 atoms per oxygen molecule. So the answer is 1.204*10^24 atoms in 1.0 mole of O2.