Answer:
D: The bond is created by oppositely charged metal and nonmetal atoms.
Explanation:
An ionic metal basically involves a metal and a nonmetal in bonding. A metal is a cation with a + charge and a nonmetal is a anion with a - charge. I will give you an example. Magnesium Chloride is a ionic bond. This is because Magnesium is a metal with a +2 charge(so it is a cation). Chloride or Chlorine is a nonmetal because it has a -1 charge.(so it is a anion). The chemical formula for magnesium chloride is MgCl2.
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Copper has a FCC i.e. face centered cubic crystal structure. The 100 plane is essentially a planar section of the cubic cell where 4 Cu atoms occupy the 4 corners of the plane along with 1 Cu atom at the center of that plane. Each of the Cu atoms in the corners is shared by 4 adjacent unit cells. Thus, there are 2 Cu atoms present in the 100 plane (4*1/4 + 1 = 2).
Now, the planar density PD along the 100 plane is given as:
PD(100) = # atoms in the 100 plane/Area of 100 plane
=
Here R = radius = 0.128 nm = 
PD = 
Most definitely gravity. Gravity is what makes things go up and or down